Extreme weather events are rare, but disproportionately important for societal and economic risk. Estimating their likelihood is therefore central to applications ranging from infrastructure design to financial risk management. This task is fundamentally constrained by limited data. Observational records are often too short to robustly characterize rare events, while the underlying climate system is changing in ways that can alter the behavior of extremes. At the same time, statistical approaches for estimating extreme event probabilities and physical studies of the processes that generate extremes are often developed separately, limiting our ability to interpret risk in a coherent framework. This thesis investigates how statistical limitations and physical climate processes jointly shape the estimation and interpretation of extreme events under limited data conditions. Using a combination of idealized climate model simulations, observational datasets, and statistical analysis, I examine both the reliability of extreme value estimates and the mechanisms that influence climate extremes, with a focus on extreme heat.
\r\n\r\nI show that short climate records can lead to systematic underestimation of rare event probabilities and large uncertainty in return level estimates. These results quantify how sample size and tail behavior constrain the reliability of statistical inference and provide guidance for identifying when available data are insufficient for robust estimation, including under climate change imposing unknown trends. I also demonstrate that observed changes in the frequency of extreme heat are, to first order, consistent with shifts in the underlying temperature distribution. A novel statistical method of isolating low-frequency variability from noisy climate data yields a simple and generalizable interpretation of observed temperature trends. Finally, I show that in regions with strong land\u2013atmosphere coupling, such as the Central United States, soil moisture deficits and atmospheric circulation patterns can amplify extreme heat beyond what occurs on typical days. These nonlinear processes influence extreme events in a way that may be challenging to anticipate at long timescales in the future. These results highlight both the limits of statistical inference for rare events and the role of physical mechanisms in shaping extreme behavior. This dissertation provides practical and conceptual tools for interpreting and quantifying extremes under limited data in a changing climate.
", "doi": "10.7907/pmnh-6875", "publication_date": "2026", "thesis_type": "phd", "thesis_year": "2026" }, { "id": "thesis:17776", "collection": "thesis", "collection_id": "17776", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:11252025-215953680", "type": "thesis", "title": "Interactions between Near-Inertial Waves and Ocean Turbulence", "author": [ { "family_name": "Conn", "given_name": "Scott", "orcid": "0000-0003-1404-0196", "clpid": "Conn-Scott" } ], "thesis_advisor": [ { "family_name": "Callies", "given_name": "Joern", "orcid": "0000-0002-6815-1230", "clpid": "Callies-J" } ], "thesis_committee": [ { "family_name": "Schneider", "given_name": "Tapio", "orcid": "0000-0001-5687-2287", "clpid": "Schneider-T" }, { "family_name": "Thompson", "given_name": "Andrew F.", "orcid": "0000-0003-0322-4811", "clpid": "Thompson-A-F" }, { "family_name": "Thomas", "given_name": "Leif N.", "orcid": "0000-0002-0548-5786", "clpid": "Thomas-L-N" }, { "family_name": "Callies", "given_name": "Joern", "orcid": "0000-0002-6815-1230", "clpid": "Callies-J" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "When atmospheric storms sweep across the sea surface they excite near-inertial waves (NIWs) whose frequency sits close to the local Coriolis frequency. By generating shear-driven mixing in the upper ocean, NIWs mediate the storm\u2013ocean coupling and, in turn, influence climate. Oceanographers have long known that the fate of wind-generated NIWs hinges on how they interact with the background circulation -- especially with mesoscale eddies -- but observations show that this interaction ranges from negligible to dominant depending on location. Those regional contrasts matter: eddy-modified NIWs can dramatically reshape the pattern and intensity of mixing. My thesis uses a mix of theory, observations, and numerical modelling to better understand the dynamics that governs NIW-mesoscale interactions.
\r\n\r\nIn trying to understand how NIWs behave in the presence of mesoscale eddies, the work of theoreticians culminated in the YBJ (Young and Ben-Jelloul) equation which describes the evolution of NIWs, including the physics of advection and refraction of NIWs by mesoscale eddies. I test whether this equation, subject to observations of the wind stress, stratification and mesoscale eddy field, can capture the observed dynamics of NIWs. Simulations of the YBJ equation can be compared to observations from a mooring array in the North Atlantic. The simulation reproduces the amplitude, phase, and across-array structure of the waves, and it reveals strong concentration of NIWs in anticyclones. In contrast, the traditional slab model -- lacking mesoscale interaction physics -- performs poorly. Potential energy budget diagnostics further show that, in this region, the net NIW\u2013eddy energy exchange is small compared to other terms in the mesoscale energy budget.
\r\n\r\nGiven the utility of the YBJ equation in understanding observations, I next try to understand theoretically what governs the impact that mesoscale eddies have on NIWs. This analysis heavily leverages the connection between the YBJ equation and the Schr\u00f6dinger equation of quantum mechanics. The key governing parameter in the YBJ equation is the wave dispersiveness which quantifies the ratio of wave dispersion to wave refraction. Analytical calculations of the eigenmodes of the YBJ equation show that strongly dispersive waves are marginally affected by the eddies. However, eddies strongly imprint onto weakly dispersive NIWs. In the weak dispersion limit, the ray-tracing equations emerge from the YBJ equation, resolving some controversies regarding the applicability of ray-tracing to NIWs.
\r\n\r\nFinally, I try to understand how these different regimes may be distributed throughout the ocean. Observations from the Global Drifter Program can be used to calculate NIW spectra. Separating these spectra by vorticity reveals the impact of NIW-mesoscale interactions. NIW frequency shifts correlate strongly with vorticity, signalling weakly dispersive dynamics. Only a patch of the North Pacific shows a muted impact of mesoscale eddies. In high energy regions, such as western boundary currents and the Antarctic Circumpolar Current, NIWs exhibit a net negative frequency shift -- a potential sign of strongly dispersive waves. The true NIW signal is composed of many wave modes, each with a different dispersiveness, and each contributing to the observations. Idealised simulations of the YBJ equation are able to replicate the observed spectra from drifters well. The eigenmode approach is also useful in understanding the underlying physics that results in the observed spectral characteristics. The drifters confirm that trapping in anticyclones is common, but not universal.
", "doi": "10.7907/z5n5-s931", "publication_date": "2026", "thesis_type": "phd", "thesis_year": "2026" }, { "id": "thesis:17390", "collection": "thesis", "collection_id": "17390", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06032025-003651371", "primary_object_url": { "basename": "PhD_Thesis__Polina_Khapikova_.pdf", "content": "final", "filesize": 30711121, "license": "other", "mime_type": "application/pdf", "url": "/17390/1/PhD_Thesis__Polina_Khapikova_.pdf", "version": "v7.0.0" }, "type": "thesis", "title": "From Hadley Cells to Heat Extremes: Novel Physical and Statistical Frameworks for Evaluating Climate Models", "author": [ { "family_name": "Khapikova", "given_name": "Polina", "orcid": "0000-0001-8142-5577", "clpid": "Khapikova-Polina" } ], "thesis_advisor": [ { "family_name": "Schneider", "given_name": "Tapio", "orcid": "0000-0001-5687-2287", "clpid": "Schneider-T" } ], "thesis_committee": [ { "family_name": "Thompson", "given_name": "Andrew F.", "orcid": "0000-0003-0322-4811", "clpid": "Thompson-A-F" }, { "family_name": "Schneider", "given_name": "Tapio", "orcid": "0000-0001-5687-2287", "clpid": "Schneider-T" }, { "family_name": "Frankenberg", "given_name": "Christian", "orcid": "0000-0002-0546-5857", "clpid": "Frankenberg-Christian" }, { "family_name": "Baldwin", "given_name": "Jane", "orcid": "0000-0002-4174-2743", "clpid": "Baldwin-Jane" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "As climate models become increasingly central to projecting future climate impacts and guiding adaptation strategies, understanding the sources of intermodel spread is critical. This thesis investigates key drivers of model uncertainty through a process-based lens grounded in fundamental climate physics. It focuses on two major contributors to model spread: atmospheric circulation and land-surface processes, which together shape regional hydrological extremes and human-relevant climate outcomes.
\r\n\r\nFirst, I develop a zonal-mean energetic framework to explain variations in the meridional extent of the Hadley Circulation (HC) across seasonal, interannual, and multidecadal timescales. I show that changes in tropical net energy input and eddy energy export can be used to explain HC migrations in a variety of contexts. For example, this framework can be used to explain the larger migrations of the ascending HC branch relative to the descending branch over the seasonal cycle, and the contrasting HC migration observed during El Nino events and in response to global warming. This approach provides a physically grounded method for interpreting both observed short-term variability and projected future changes in the tropical atmospheric circulation.
\r\n\r\nNext, I address uncertainty in terrestrial water storage (TWS) trends across CMIP6 models. To circumvent the limitations of short observational records, I introduce a novel method that compares the seasonal cycle of TWS using empirical orthogonal functions derived from GRACE satellite data. This approach enables the ranking of models based on their fidelity to observed seasonal variability. Models with stronger agreement with GRACE observations exhibit more consistent and often larger trends in TWS, and share features such as deeper soils and spatially distinct precipitation patterns. These insights can guide model selection and development efforts.
\r\n\r\nFinally, I explore model spread in the temperature-humidity combinations that produce extreme wet-bulb temperatures (WBTs), a key metric of human heat stress. While WBT projections are relatively consistent across models, the partitioning between temperature and humidity\u2014quantified using the \"stickiness\" metric\u2014varies substantially. I show that these differences lead to large uncertainty in the physiological impacts of heat stress at a given WBT. This work underscores the importance of accurately capturing surface energy partitioning to constrain present and future heat stress risks.
\r\n\r\nTogether, the chapters of this thesis offer several innovative approaches to evaluating uncertainty in climate projections. By applying simple theory, observational constraints, and novel metrics, this work demonstrates how physically grounded methods can identify more reliable models and improve the accuracy of future climate projections---particularly for hydrological extremes and human-centered impacts.
", "doi": "10.7907/px1t-j224", "publication_date": "2025", "thesis_type": "phd", "thesis_year": "2025" }, { "id": "thesis:16700", "collection": "thesis", "collection_id": "16700", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:09062024-191128914", "type": "thesis", "title": "Observational and Computational Studies of Atmospheric Particle Formation", "author": [ { "family_name": "Ward", "given_name": "Ryan Xavier", "orcid": "0000-0003-2317-3310", "clpid": "Ward-Ryan-Xavier" } ], "thesis_advisor": [ { "family_name": "Seinfeld", "given_name": "John H.", "orcid": "0000-0003-1344-4068", "clpid": "Seinfeld-J-H" } ], "thesis_committee": [ { "family_name": "Wennberg", "given_name": "Paul O.", "orcid": "0000-0002-6126-3854", "clpid": "Wennberg-P-O" }, { "family_name": "Flagan", "given_name": "Richard C.", "orcid": "0000-0001-5690-770X", "clpid": "Flagan-R-C" }, { "family_name": "Schneider", "given_name": "Tapio", "orcid": "0000-0001-5687-2287", "clpid": "Schneider-T" }, { "family_name": "Ng", "given_name": "Nga L.", "orcid": "0000-0001-8460-4765", "clpid": "Ng-Nga-L" }, { "family_name": "Seinfeld", "given_name": "John H.", "orcid": "0000-0003-1344-4068", "clpid": "Seinfeld-J-H" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "Aerosols are a ubiquitous component of the atmosphere, playing pivotal roles in air quality and climate. This thesis explores the way these particles come to be, and their roles in these atmospheric processes.
\r\n\r\nAerosols form from a variety of anthropogenic and biogenic activities, processes which are very prominent in urban settings. In Los Angeles, the last decade of research has been dominated by the role of summertime secondary organic aerosol (SOA) in contributing to particulate matter (PM). Here, we make observations in the equinox seasons and in the winter and detail the formation of atmospheric aerosols in these seasons. Using aerosol mass spectrometry, we demonstrate that ammonium nitrate persists as one of the dominant secondary aerosol components despite dramatic reductions in nitrogen oxide (NO\u2093) emissions. Further, we show that this ammonium nitrate is not measured by routine air quality measurements, biasing regulatory PM2.5 measurements. In the wintertime, similar techniques demonstrate that primary organic aerosol, as opposed to secondary, is an important component of the PM2.5, contrary to the prevailing narratives that SOA dominates the aerosol mass.
\r\n\r\nAt global scales, the role of these aerosols in cloud formation and climate processes is of primary interest. While a variety of physicochemical properties of aerosols are important in the formation of cloud droplets, we focus here on the specific process of organic surface-partitioning. It has been suggested that in phase-separated aerosol, organic-rich surface layers can depress the surface tension of the particles, lowering their barrier to activate into cloud droplets. We assess this propensity for surface tension depression in two SOA systems, \u03b1-pinene and \u03b2-caryophyllene. Synergizing laboratory measurements, a thermodynamic model, and field data, it is shown that surface-active organics in these SOA systems can impact their hygroscopicity, though perhaps not sufficiently to warrant inclusion of these processes in global-scale models.
", "doi": "10.7907/dham-e191", "publication_date": "2025", "thesis_type": "phd", "thesis_year": "2025" }, { "id": "thesis:16724", "collection": "thesis", "collection_id": "16724", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:09132024-172910003", "type": "thesis", "title": "Cloudy with a Chance of Microphysics: Modeling Droplet Collisions for the Climate Scale", "author": [ { "family_name": "de Jong", "given_name": "Emily Katherine", "orcid": "0000-0002-5310-4554", "clpid": "de-Jong-Emily-Katherine" } ], "thesis_advisor": [ { "family_name": "Schneider", "given_name": "Tapio", "orcid": "0000-0001-5687-2287", "clpid": "Schneider-T" } ], "thesis_committee": [ { "family_name": "Blanquart", "given_name": "Guillaume", "orcid": "0000-0002-5074-9728", "clpid": "Blanquart-G" }, { "family_name": "Colonius", "given_name": "Tim", "orcid": "0000-0003-0326-3909", "clpid": "Colonius-T" }, { "family_name": "Fu", "given_name": "Xiaojing", "orcid": "0000-0001-7120-704X", "clpid": "Fu-Xiaojing" }, { "family_name": "Morrison", "given_name": "Hugh", "orcid": "0000-0001-8480-9787", "clpid": "Morrison-Hugh" }, { "family_name": "Schneider", "given_name": "Tapio", "orcid": "0000-0001-5687-2287", "clpid": "Schneider-T" } ], "local_group": [ { "literal": "3MT Competition (Caltech)" }, { "literal": "div_eng" } ], "abstract": "Feedbacks between a warming atmosphere, emission of aerosols, and clouds and precipitation are some of the most difficult aspects for climate models to accurately capture. While climate models operate at resolutions of tens or hundreds of kilometers, many of the physics that determine how and where clouds form or precipitate function at the micron droplet scale. Due to this disparity in physical scales, most of these cloud physics must be modeled with only a few approximate quantities and physical equations. These simplifications lead to large uncertainties about climate forcings such as the sensitivity of global warming to human-emitted aerosols.
\r\n\r\nThis work presents several promising new techniques for modeling and understanding hydrometeors in the climate system, with a particular focus on processes that involve collisions between droplets. First, I extend a high-complexity high-fidelity Lagrangian microphysics method to represent the process of breakup, in which colliding droplets fragment upon collision. Next, I introduce two new methods which attempt to reduce the assumptions inherent to modeling droplet coalescence, in which colliding droplets combine to form a larger drop. The first method uses a spectral finite element approach, while the second generalizes this technique using a method of moments to create a fully flexible microphysics scheme. Finally, I turn to remote observations of clouds, aerosols, and lightning over busy shipping regions to offer new techniques for quantifying aerosol-cloud interactions from creative data resources. This combination of high-fidelity modeling tools, observational data, and efficient numerical methods offers a path toward improving our understanding of the role of cloud microphysics in our climate system.
", "doi": "10.7907/yv2y-kg55", "publication_date": "2025", "thesis_type": "phd", "thesis_year": "2025" }, { "id": "thesis:16527", "collection": "thesis", "collection_id": "16527", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06262024-011209069", "primary_object_url": { "basename": "bonan-db-dissertation.pdf", "content": "final", "filesize": 12539991, "license": "other", "mime_type": "application/pdf", "url": "/16527/1/bonan-db-dissertation.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Explications of a Changing Climate", "author": [ { "family_name": "Bonan", "given_name": "David Brooking", "orcid": "0000-0003-3867-6009", "clpid": "Bonan-David-Brooking" } ], "thesis_advisor": [ { "family_name": "Schneider", "given_name": "Tapio", "orcid": "0000-0001-5687-2287", "clpid": "Schneider-T" }, { "family_name": "Thompson", "given_name": "Andrew F.", "orcid": "0000-0003-0322-4811", "clpid": "Thompson-A-F" } ], "thesis_committee": [ { "family_name": "Adkins", "given_name": "Jess F.", "orcid": "0000-0002-3174-5190", "clpid": "Adkins-J-F" }, { "family_name": "Schneider", "given_name": "Tapio", "orcid": "0000-0001-5687-2287", "clpid": "Schneider-T" }, { "family_name": "Thompson", "given_name": "Andrew F.", "orcid": "0000-0003-0322-4811", "clpid": "Thompson-A-F" }, { "family_name": "Zanna", "given_name": "Laure", "orcid": "0000-0002-8472-4828", "clpid": "Zanna-Laure" }, { "family_name": "Rugenstein", "given_name": "Maria", "orcid": "0000-0002-4541-3277", "clpid": "Rugenstein-Maria" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "Climate models encode our collective knowledge about the climate system and are among the best tools available for estimating past and future climate change. However, in response to greenhouse gas forcing, climate models exhibit a large intermodel spread in various aspects of the climate system, adding considerable uncertainty to future climate projections. This dissertation introduces a series of conceptual models and frameworks to understand the behavior of climate models under greenhouse gas forcing and, consequently, Earth's changing climate.
\r\n\r\nA simple statistical model is used to explain and constrain the intermodel spread in Arctic sea ice projections across climate models. The probability of encountering seasonally ice-free conditions in the twenty-first century is also explored by systematically constraining components of the statistical model with observations.
\r\n\r\nA conceptual framework is introduced to understand controls on the strength and structure of the Atlantic meridional overturning circulation (AMOC) in climate models. This framework is used to explain why climate models suggest the present-day and future AMOC strength are related. This framework, in conjunction with observations, implies modest twenty-first-century AMOC weakening.
\r\n\r\nA simple energy budget framework is used to examine precipitation over a wide range of climates simulated by climate models. It is shown that in extremely hot climates, global-mean precipitation decreases despite increasing surface temperatures because of increased atmospheric shortwave absorption from water vapor, which limits energy available for surface evaporation. These results have large implications for understanding weathering rates in past climates as well as Earth's climate during the Hadean and Archaean eons.
\r\n\r\nFinally, a framework is introduced to reconcile two different approaches for quantifying the effect of climate feedbacks on surface temperature change. The framework is used to examine the influence of clouds on Arctic amplification in a climate model and an energy balance model. This work introduces an important non-local mechanism for Arctic amplification and shows that constraining the mid-latitude cloud feedback will greatly reduce the intermodel spread in Arctic warming.
\r\n\r\nThis dissertation advances our understanding of various aspects of Earth's changing climate and provides a series of conceptual frameworks that can be used to further constrain the behaviour of climate models in response to external forcing.
", "doi": "10.7907/afb5-ns06", "publication_date": "2025", "thesis_type": "phd", "thesis_year": "2025" }, { "id": "thesis:16895", "collection": "thesis", "collection_id": "16895", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:12032024-211328064", "primary_object_url": { "basename": "Caltech_Dissertation_v3_Final.pdf", "content": "final", "filesize": 12342692, "license": "other", "mime_type": "application/pdf", "url": "/16895/1/Caltech_Dissertation_v3_Final.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Towards Hybrid Physics-Machine Learning Parameterizations: Employing Data Assimilation for Online Learning of Turbulence and Convection Closures in a Unified Scheme", "author": [ { "family_name": "Christopoulos", "given_name": "Costa", "orcid": "0000-0002-8552-465X", "clpid": "Christopoulos-Costa" } ], "thesis_advisor": [ { "family_name": "Schneider", "given_name": "Tapio", "orcid": "0000-0001-5687-2287", "clpid": "Schneider-T" } ], "thesis_committee": [ { "family_name": "Frankenberg", "given_name": "Christian", "orcid": "0000-0002-0546-5857", "clpid": "Frankenberg-Christian" }, { "family_name": "Schneider", "given_name": "Tapio", "orcid": "0000-0001-5687-2287", "clpid": "Schneider-T" }, { "family_name": "Ross", "given_name": "Zachary E.", "orcid": "0000-0002-6343-8400", "clpid": "Ross-Z-E" }, { "family_name": "Beucler", "given_name": "Tom", "orcid": "0000-0002-5731-1040", "clpid": "Beucler-Tom" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "Despite advances in climate modeling, the spread in equilibrium climate sensitivity estimates has remained largely unchanged over generations of modeling, mainly due to uncertainties in cloud feedback mechanisms arising from subgrid-scale turbulence, convection, clouds, and the resulting cloud-radiation interactions. Misrepresentations of these processes affect both long-term climate projections and the simulation of short-term atmospheric phenomena, such as the diurnal cycle of precipitation. These limitations are most pronounced in regimes like stratocumulus clouds and their transition to cumulus over ocean basins---areas where climate models have the largest cloud biases in the historical record. This thesis aims to constrain the critical subgrid-scale physics of turbulence and convection by developing and calibrating a hybrid physics\u2013machine learning parameterization using the Eddy-diffusivity Mass-flux (EDMF) framework. By integrating machine learning components into the EDMF and employing data assimilation techniques for online learning, we attempt to directly target some of the processes responsible for uncertainties in cloud feedbacks.\r\n\r\nIn this thesis, we employ ensemble Kalman inversion within a single-column setup to simultaneously perform online calibration of parameters in empirical closures and embedded neural networks, targeting large-eddy simulations as ground truth. The online learning framework ensures stability and physical consistency, as machine learning components are trained within the context of the full model dynamics. By directly targeting poorly constrained processes like lateral entrainment/detrainment and turbulent mixing lengths, we improve the representation of subgrid-scale fluxes and resulting cloud properties across various atmospheric regimes. We uncover limitations of traditional semi-empirical closures, providing insights for future model development. The calibrated hybrid parameterization outperforms existing schemes, particularly in regions where climate models have historically underperformed, and maintains accuracy in out-of-sample forcings from a warmer climate. This work demonstrates that integrating machine learning with physics-based parameterizations through data assimilation offers a systematic and robust approach for reducing biases in climate models and understanding the physics of elusive subgrid-scale closures.", "doi": "10.7907/ptr2-0r80", "publication_date": "2025", "thesis_type": "phd", "thesis_year": "2025" }, { "id": "thesis:15158", "collection": "thesis", "collection_id": "15158", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05092023-230615398", "type": "thesis", "title": "The Role of Small-Scale Cloud, Aerosol, and Radiation Processes for Earth's Climate", "author": [ { "family_name": "Singer", "given_name": "Clare Emilie Elmendorf", "orcid": "0000-0002-1708-0997", "clpid": "Singer-Clare-Emilie-Elmendorf" } ], "thesis_advisor": [ { "family_name": "Schneider", "given_name": "Tapio", "orcid": "0000-0001-5687-2287", "clpid": "Schneider-T" } ], "thesis_committee": [ { "family_name": "Wennberg", "given_name": "Paul O.", "orcid": "0000-0002-6126-3854", "clpid": "Wennberg-P-O" }, { "family_name": "Schneider", "given_name": "Tapio", "orcid": "0000-0001-5687-2287", "clpid": "Schneider-T" }, { "family_name": "Callies", "given_name": "Joern", "orcid": "0000-0002-6815-1230", "clpid": "Callies-J" }, { "family_name": "Feingold", "given_name": "Graham", "orcid": "0000-0002-0774-2926", "clpid": "Feingold-Graham" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "What makes clouds ethereal and beautiful also makes them complex and challenging to understand and to model. The important (thermo)dynamical processes of clouds occur at scales from microns (cloud-aerosol interactions), to meters (turbulence), to thousands of kilometers (synoptic weather patterns), and every scale in between. In this thesis, I explore several facets of how clouds interact with, respond to, and shape Earth's climate. I focus on small-scale processes, using high-resolution models and theory, to understand phenomena that can have large-scale impacts.
\r\n \r\nIn the first three chapters of this thesis, I explore the idea of stratocumulus-cumulus transitions. Chapters 1 and 2 develop and demonstrate a conceptual model of a cloud-topped atmospheric boundary layer, which is rooted in mixed-layer theory. This model is able to concisely explain both the spatial stratocumulus-cumulus transition observed in the historical period, as well as a transition that has only been hypothesized by models, which may occur in the future as the direct effect of extreme concentrations of atmospheric CO2, or which may have occurred in the past. I use this conceptual model to show the importance of sea surface temperature variations for driving the climatological transition, and on sea surface warming as a positive feedback for the CO2-induced transition. Chapter 3 extends this work to understand the global response to CO2-induced stratocumulus-cumulus transitions and the role for spatial teleconnections by embedding this conceptual model of the boundary layer into a global climate model (GCM). In the GCM we see both a fast adjustment in low cloud cover to CO2, as well as a slower surface temperature-mediated feedback. Under CO2 quadrupling, the stratocumulus cloud regions shrink in extent as the cloud-top longwave cooling is inhibited by CO2 and surface temperatures also increase.
\r\n\r\nThe final two chapters diverge from the previous theme to present two studies using very high-resolution models to explore how clouds interact with i) aerosols and ii) radiation. In Chapter 4, using a particle-based cloud microphysics model, I find that aerosol hygroscopicity, determined by the chemical composition of the particles, can alter stratocumulus cloud macrophysical properties, like liquid water path by up to 25% (in the regime of small aerosol sizes). I compare these results to a more standard moment-based microphysics model and find that this model is overly sensitive to aerosol hygroscopicity in the regime of small aerosol sizes, but realistically represents the negative sensitivity for large aerosol sizes. Finally, in Chapter 5, I use a Monte Carlo 3D radiative transfer solver to estimate the global albedo bias introduced in models which make the standard assumption that photon fluxes in the horizontal are zero (the so-called Independent Column Approximation). I extrapolate globally from a set of resolved tropical cloud fields, using a learned empirical relation between top-of-atmosphere flux bias and cloud water path. I conclude that in a global model that resolves clouds at small-enough spatial scales, the tropical-mean, annual-mean bias may be on the order of 3 W m-2.
", "doi": "10.7907/bd4s-w586", "publication_date": "2024", "thesis_type": "phd", "thesis_year": "2024" }, { "id": "thesis:16156", "collection": "thesis", "collection_id": "16156", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:08112023-233852985", "primary_object_url": { "basename": "thesis_aug15.pdf", "content": "final", "filesize": 2646989, "license": "other", "mime_type": "application/pdf", "url": "/16156/1/thesis_aug15.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "From Source to Sink: Measuring and Modeling Processes Affecting Methane Emissions and Loss", "author": [ { "family_name": "Nguyen", "given_name": "Newton Huy", "orcid": "0000-0002-9118-8672", "clpid": "Nguyen-Newton-Huy" } ], "thesis_advisor": [ { "family_name": "Frankenberg", "given_name": "Christian", "orcid": "0000-0002-0546-5857", "clpid": "Frankenberg-Christian" } ], "thesis_committee": [ { "family_name": "Wennberg", "given_name": "Paul O.", "orcid": "0000-0002-6126-3854", "clpid": "Wennberg-P-O" }, { "family_name": "Yung", "given_name": "Yuk L.", "orcid": "0000-0002-4263-2562", "clpid": "Yung-Y-L" }, { "family_name": "Schneider", "given_name": "Tapio", "orcid": "0000-0001-5687-2287", "clpid": "Schneider-T" }, { "family_name": "Frankenberg", "given_name": "Christian", "orcid": "0000-0002-0546-5857", "clpid": "Frankenberg-Christian" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "Methane is a key target for climate change mitigation efforts. With a radiative forcing 85 times stronger than CO\u2082 over a 20-year period and an atmospheric lifespan of only a decade, mitigating methane emissions will slow climate change in the near-term. However, quantifying methane emissions from specific sectors accurately poses a significant challenge. This is because top-down estimations of methane emissions demand precise observations and constraints on a range of physical and chemical processes. In this thesis, I seek to enhance the accuracy of methane emissions calculations by resolving these processes in detail and advocating for an expansion of the methane monitoring network.
\r\n\r\nThe primary mechanism for atmospheric methane destruction is its oxidation by the Hydroxyl radical (OH). Chemical feedbacks due to temporal variations in OH availability can substantially influence the methane lifetime and, consequently, emissions trends over recent decades. In Chapter 2, I quantify the impact of this predominant chemical loss mechanism on methane emissions calculations.
\r\n\r\nMethane loss to the stratosphere represents the second most significant methane destruction mechanism, although the processes involved remain highly uncertain. Accurately quantifying methane loss via stratospheric-tropospheric exchange is crucial for improving the accuracy of methane emissions calculations. In Chapter 3, I utilize chemical tracers to determine how stratospheric-tropospheric exchange influences global methane emissions trends.
\r\n\r\nCurrent understanding of greenhouse gas fluxes from a top-down perspective typically relies on atmospheric inversions, which depend on spatial and temporal gradients in observed greenhouse gas concentrations. However, maintaining highly accurate ground-based measurements poses logistical and financial challenges, while satellites currently do not provide the requisite accuracy and spatial resolution for long-term monitoring. In Chapter 4, I explore the potential of frequency combs in measuring environmental impacts on greenhouse gas sensing and as tools to expand the observation network.
\r\n\r\nIn summary, this thesis contributes to a more profound understanding of the two primary methane sinks and how their variations affect methane emissions trends over recent decades. It also lays the groundwork for the next-generation greenhouse gas observation network using laser frequency combs by quantifying environmental impacts on greenhouse gas spectroscopy directly in the field. Future advances should focus on a more accurate understanding of methane sink processes, improved spectroscopy, and expanded measurement networks. This will require advances in both modeling and measurements.
\r\n\r\nUltimately, rapid and efficient mitigation of methane emissions remains the most feasible approach to curb anthropogenic climate change. To do this however, accurate assessments of methane trends and emissions necessitate bringing methane measurements and modeling of methane destruction processes closer to the real world.
", "doi": "10.7907/k2d1-rn95", "publication_date": "2024", "thesis_type": "phd", "thesis_year": "2024" }, { "id": "thesis:16512", "collection": "thesis", "collection_id": "16512", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06082024-115947714", "primary_object_url": { "basename": "thesis.pdf", "content": "final", "filesize": 17017374, "license": "other", "mime_type": "application/pdf", "url": "/16512/1/thesis.pdf", "version": "v6.0.0" }, "type": "thesis", "title": "Kernel Methods for Learning About Complex Dynamical Systems", "author": [ { "family_name": "Burov", "given_name": "Dmitry Anatolyevich", "orcid": "0000-0002-5060-6794", "clpid": "Burov-Dmitry-Anatolyevich" } ], "thesis_advisor": [ { "family_name": "Stuart", "given_name": "Andrew M.", "orcid": "0000-0001-9091-7266", "clpid": "Stuart-A-M" } ], "thesis_committee": [ { "family_name": "Owhadi", "given_name": "Houman", "orcid": "0000-0002-5677-1600", "clpid": "Owhadi-H" }, { "family_name": "Stuart", "given_name": "Andrew M.", "orcid": "0000-0001-9091-7266", "clpid": "Stuart-A-M" }, { "family_name": "Schneider", "given_name": "Tapio", "orcid": "0000-0001-5687-2287", "clpid": "Schneider-T" }, { "family_name": "Hoffmann", "given_name": "Franca", "orcid": "0000-0002-1182-5521", "clpid": "Hoffmann-Franca" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "The ubiquitous spread of machine learning tools in natural sciences in recent years has seen trully exponential growth. What sounded like an expression from a sci-fi novel mere 7 years ago, \"solving PDEs with machine learning\" is hardly surprising to anyone today. The variety of methods is very large, but most of them revolve around the artificial neural networks. Despite tremendous success of applications to problems in natural sciences, and despite many strides towards a fundamental theory of neural networks, they still often lack interpretability and robustness of the results. An alternative, much narrower class of machine learning algorithms is comprised of the kernel methods. These methods, in contrast, offer deep analytical theory, with many approximation results and interpretable components. The firm foundation of the kernel methods, however, is offset by the practical difficulties, such as high computational cost, the burden of high-dimensional optimization and the necessity to manually choose kernel parametrization. This thesis explores a few applications of the kernel methods to dynamical systems, with the goal to address some of those issues. The comparison between the kernel analog forecasting and the plain Gaussian process regression is made, both from theoretical and practical sides, and a parametric extension of the former is proposed. An application of kernel methods to closures of dynamical systems is showcased. Finally, an application of data assimilation machinery to an epidemiological model is shown.
", "doi": "10.7907/zmmv-1a93", "publication_date": "2024", "thesis_type": "phd", "thesis_year": "2024" }, { "id": "thesis:14999", "collection": "thesis", "collection_id": "14999", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:08112022-214313625", "primary_object_url": { "basename": "Cheng_Rui_2023_thesis (1).pdf", "content": "final", "filesize": 36258632, "license": "other", "mime_type": "application/pdf", "url": "/14999/1/Cheng_Rui_2023_thesis (1).pdf", "version": "v6.0.0" }, "type": "thesis", "title": "Remotely Evaluating the Seasonality of Gross Primary Production at High Latitudes", "author": [ { "family_name": "Cheng", "given_name": "Rui", "orcid": "0000-0002-3003-8339", "clpid": "Cheng-Rui" } ], "thesis_advisor": [ { "family_name": "Frankenberg", "given_name": "Christian", "orcid": "0000-0002-0546-5857", "clpid": "Frankenberg-Christian" } ], "thesis_committee": [ { "family_name": "Schneider", "given_name": "Tapio", "orcid": "0000-0001-5687-2287", "clpid": "Schneider-T" }, { "family_name": "Frankenberg", "given_name": "Christian", "orcid": "0000-0002-0546-5857", "clpid": "Frankenberg-Christian" }, { "family_name": "Wennberg", "given_name": "Paul O.", "orcid": "0000-0002-6126-3854", "clpid": "Wennberg-P-O" }, { "family_name": "Bloom", "given_name": "A. Anthony", "clpid": "Bloom-A-Anthony" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "A warming trend larger than the global average is changing high-latitude terrestrial ecosystems. The impact of climate change at high latitudes is especially notable on the seasonality of vegetation photosynthesis, such as the Arctic greening, lengthened growing season, and increased peak production in the growing season. As a critical component of the global carbon cycle and land carbon sink, continuously monitoring the seasonal trajectory of ecosystem-level photosynthesis, Gross Primary Production (GPP), is much needed to better understand the climate change impacts and the sensitivity of high-latitude plant communities under global climate change. GPP has been estimated from both ground and space. However, sparsely distributed ground-level measurements are not representative of heterogeneous land cover and complex terrain in high latitudes. Remote sensing techniques provide extensive spatial coverage for comparing GPP at the regional scale. In this thesis, I carefully examine the advances in remote sensing for monitoring GPP at high latitudes, including using hyperspectral reflectance and Solar-Induced chlorophyll Fluorescence (SIF). We show that reflectance near 531 nm can track the seasonality of Light Use Efficiency (LUE), complementing conventional normalized difference vegetation index which is only a proxy of Absorbed Photosynthetic Active Radiation (APAR). Tracking both LUE and APAR is critical for improving GPP estimation, especially in evergreen forests with photosynthetic phenology but sustained canopy color -- a typical land cover type at high latitudes. Satellite-measured SIF can also track both LUE and APAR. Here, it is shown that the empirical model predicting GPP using SIF is land cover dependent. The presence of snow and surface, heterogeneous land cover, and complex terrains in the high latitudes further complicate the interpretation of the SIF-GPP relationship. To improve the accuracy of interpreting SIF in complex terrain, a geometric model is developed to account for variations in APAR on tilted slopes. The results of this thesis enhance the use of both reflectance and SIF to help improve terrestrial biosphere models simulating GPP and cope with model-data uncertainties. The results are also a useful reference for future satellite missions designing instruments and correcting topographic impacts. Overall, this thesis contributes to better evaluating GPP and constraining climate projection uncertainties.
", "doi": "10.7907/3gnn-sy17", "publication_date": "2023", "thesis_type": "phd", "thesis_year": "2023" }, { "id": "thesis:15063", "collection": "thesis", "collection_id": "15063", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:11152022-215747755", "primary_object_url": { "basename": "PhD_thesis__Ignacio_Lopez_Gomez_-revised.pdf", "content": "final", "filesize": 28614789, "license": "other", "mime_type": "application/pdf", "url": "/15063/1/PhD_thesis__Ignacio_Lopez_Gomez_-revised.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "A Unified Data-Informed Model of Turbulence and Convection for Climate Prediction", "author": [ { "family_name": "L\u00f3pez G\u00f3mez", "given_name": "Ignacio", "orcid": "0000-0002-7255-5895", "clpid": "L\u00f3pez-G\u00f3mez-Ignacio" } ], "thesis_advisor": [ { "family_name": "Schneider", "given_name": "Tapio", "orcid": "0000-0001-5687-2287", "clpid": "Schneider-T" } ], "thesis_committee": [ { "family_name": "Callies", "given_name": "Joern", "orcid": "0000-0002-6815-1230", "clpid": "Callies-J" }, { "family_name": "Stuart", "given_name": "Andrew M.", "orcid": "0000-0001-9091-7266", "clpid": "Stuart-A-M" }, { "family_name": "Teixeira", "given_name": "Joao", "clpid": "Teixeira-Joao" }, { "family_name": "Schneider", "given_name": "Tapio", "orcid": "0000-0001-5687-2287", "clpid": "Schneider-T" } ], "local_group": [ { "literal": "Resnick Sustainability Institute" }, { "literal": "div_gps" } ], "abstract": "Resolving atmospheric turbulent and convective processes in global climate simulations is, and will remain for decades, an intractable computational problem. The strong influence of these processes on cloud formation and maintenance makes the task of modeling turbulence and convection one of the grand challenges in climate modeling, due to the outsized effect of clouds on climate. Current operational climate models fail to represent atmospheric turbulence and convection accurately and consistently across dynamical regimes and vertical levels; errors in the representation of these processes explain about half of the spread in climate projections. This dissertation seeks to reduce such representation errors by improving a recently proposed unified framework for modeling turbulence and convection, known as the extended eddy-diffusivity mass-flux scheme, in several ways. First, the framework is rederived by systematically coarse-graining the governing fluid equations, highlighting the assumptions about atmospheric motion that are necessary to yield the scheme. New terms related to turbulent entrainment processes are shown to arise from the derivation. Second, a generalized formulation of turbulent diffusion consistent with the framework is presented. This novel formulation is shown to accurately represent turbulent processes under statically stable and unstable conditions, including regimes with sharp lapse rate inversions such as the stratocumulus-topped boundary layer. Finally, a methodology to calibrate free parameters within the model from indirect data is proposed. The methodology, based on Kalman filtering, is shown to be efficient at calibrating imperfect black-box models from noisy data, and in its regularized unscented version approximately quantifies parametric uncertainty. The resulting unified data-informed model of turbulence and convection is shown to accurately represent a range of low-cloud regimes that are associated with the largest biases in current operational climate models. The response of the model to realistic climate perturbations is also shown to be consistent with the resolved climate response, although structural errors in the amount of condensate are still important at realistic vertical resolutions.", "doi": "10.7907/042m-9686", "publication_date": "2023", "thesis_type": "phd", "thesis_year": "2023" }, { "id": "thesis:14313", "collection": "thesis", "collection_id": "14313", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:07262021-194514668", "type": "thesis", "title": "Atmospheric and Ocean Dynamics of Water Worlds", "author": [ { "family_name": "de Oliveira Lobo", "given_name": "Ana Helena", "orcid": "0000-0003-3862-1817", "clpid": "de-Oliveira-Lobo-Ana-Helena-de-Oliveira" } ], "thesis_advisor": [ { "family_name": "Bordoni", "given_name": "Simona", "orcid": "0000-0003-4771-3350", "clpid": "Bordoni-S" } ], "thesis_committee": [ { "family_name": "Thompson", "given_name": "Andrew F.", "orcid": "0000-0003-0322-4811", "clpid": "Thompson-A-F" }, { "family_name": "Schneider", "given_name": "Tapio", "orcid": "0000-0001-5687-2287", "clpid": "Schneider-T" }, { "family_name": "Knutson", "given_name": "Heather A.", "orcid": "0000-0002-5375-4725", "clpid": "Knutson-H-A" }, { "family_name": "Bordoni", "given_name": "Simona", "orcid": "0000-0003-4771-3350", "clpid": "Bordoni-S" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "This dissertation explores the fundamental dynamics that control atmospheric and ocean circulation on water worlds. These planets are defined by the presence of liquid water, which is a minimum requirement for life as we know it, making them compelling targets in the search for extraterrestrial life. This work begins by examining the atmospheric features and surface climates of Earth-like planets with surface liquid water (Chapters I-III). These atmospheres are driven by top-of-atmosphere radiative imbalance. To further our understanding of planetary climate and of the atmosphere\u2019s dynamical controls, particularly with regards to seasonal behavior, we examine the circulation, energy budget, and hydrological cycle responses to changes in shortwave and longwave radiative forcings. This dissertation also explores icy worlds (Chapters IV-V), a type of water world where a liquid water ocean hides beneath a substantial icy shell. Processes occurring at the ocean boundaries can shape the circulation dynamics, stratification, and subsequent heat and salt distributions in the ocean interior. This work presents a new model for exploring these oceans, focusing on ocean-ice interactions and freshwater forcings on Enceladus.
", "doi": "10.7907/skh2-tp72", "publication_date": "2022", "thesis_type": "phd", "thesis_year": "2022" }, { "id": "thesis:14554", "collection": "thesis", "collection_id": "14554", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:04192022-173428410", "primary_object_url": { "basename": "hui_katrina_thesis_final.pdf", "content": "final", "filesize": 14791489, "license": "other", "mime_type": "application/pdf", "url": "/14554/1/hui_katrina_thesis_final.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "Monsoonal Precipitation in a Model Hierarchy: Impact of Continental Geometry and Global Warming", "author": [ { "family_name": "Hui", "given_name": "Katrina Lynn", "orcid": "0000-0003-0325-8800", "clpid": "Hui-Katrina-Lynn" } ], "thesis_advisor": [ { "family_name": "Bordoni", "given_name": "Simona", "orcid": "0000-0003-4771-3350", "clpid": "Bordoni-S" } ], "thesis_committee": [ { "family_name": "Schneider", "given_name": "Tapio", "orcid": "0000-0001-5687-2287", "clpid": "Schneider-T" }, { "family_name": "Bordoni", "given_name": "Simona", "orcid": "0000-0003-4771-3350", "clpid": "Bordoni-S" }, { "family_name": "Thompson", "given_name": "Andrew F.", "orcid": "0000-0003-0322-4811", "clpid": "Thompson-A-F" }, { "family_name": "Su", "given_name": "Hui", "orcid": "0000-0003-1265-9702", "clpid": "Su-Hui" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "Monsoon systems around the world vary in their onset timing and precipitation spatial extent, suggesting that continental geometry could play an important role in differentiating between different monsoons systems. Since over half the world's population is dependent on monsoonal precipitation, it is of crucial importance to understand what controls the strength, seasonal evolution, and spatial extent of the tropical circulation and its associated precipitation and how they will evolve in a warmer climate. Recent studies suggest that individual monsoon regions will respond differently to climate change, highlighting the potential influence continental geometry may have on the current and future monsoon. In this thesis, we study the response of monsoonal precipitation, in its precipitation intensity, pattern, and onset timing, to idealized continent and climate change using a model hierarchy. By progressively building up complexity, we can gain insight from the idealized cases to determine responsible mechanisms in the responses to warming found in individual monsoon regions within the full general circulation models (GCMs).
\r\n\r\nFirst, we study the influence of continental geometry on the timing and spatial distribution of monsoonal precipitation under our current climate using an idealized aquaplanet model run with different zonally symmetric configurations of Northern Hemispheric land. We show that having continent extending to the tropical latitudes is necessary to generate monsoons that feature a rapid migration of the convergence zone over the continent, similar to observed monsoons. Without these regions, the tropical circulation is not able to rapidly transition into an angular momentum conserving monsoon regime. Next, we focus only on the effect of climate warming on the monsoon by using a set of idealized aquaplanet simulations with uniform mixed-layer depth, run with different atmospheric longwave optical depths to simulate a large range of both colder and warmer climates than the current climate. We show that as the climate warms, during the spring the atmospheric energy storage increases, which compensates the thermal forcing and allows for the tropical circulation transitions to be delayed, resulting in a delay in monsoon onset. Furthermore, we find that in extremely warm climates, the compensating effect of the energy storage is limited due to complex changes in the surface temperature seasonality. As a result, eventually the monsoon onset delay with warming saturates. These results highlight the important role the surface, both in its physical conditions and energy balance, has on setting the monsoon.
", "doi": "10.7907/k35s-mr12", "publication_date": "2022", "thesis_type": "phd", "thesis_year": "2022" }, { "id": "thesis:14461", "collection": "thesis", "collection_id": "14461", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:01032022-071943237", "type": "thesis", "title": "Radiation-Based Analytic Approaches to Investigate the Earth\u2019s Atmosphere", "author": [ { "family_name": "Le", "given_name": "Tianhao", "orcid": "0000-0002-6600-8270", "clpid": "Le-Tianhao" } ], "thesis_advisor": [ { "family_name": "Yung", "given_name": "Yuk L.", "orcid": "0000-0002-4263-2562", "clpid": "Yung-Y-L" } ], "thesis_committee": [ { "family_name": "Wennberg", "given_name": "Paul O.", "orcid": "0000-0002-6126-3854", "clpid": "Wennberg-P-O" }, { "family_name": "Yung", "given_name": "Yuk L.", "orcid": "0000-0002-4263-2562", "clpid": "Yung-Y-L" }, { "family_name": "Schneider", "given_name": "Tapio", "orcid": "0000-0001-5687-2287", "clpid": "Schneider-T" }, { "family_name": "Frankenberg", "given_name": "Christian", "orcid": "0000-0002-0546-5857", "clpid": "Frankenberg-Christian" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "Radiation, propagating through Earth\u2019s atmosphere, plays an important role in the Earth system. Solar radiation is the major source of energy, followed by thermal infrared radiation emitted by the Earth. The total radiative energy budget affects dynamic, thermodynamics, photochemical and biological processes. In addition, by measuring the reflected and emitted radiation at a distance (e.g., satellite or aircraft), we can detect and monitor the physical characteristics of a region which can help researchers get a better understanding of Earth\u2019s atmosphere. Therefore, radiation-based analytic approaches are powerful tools in Earth Science. This thesis focuses on using radiation-based analytic tools to study the Earth\u2019s atmosphere and to understand human impacts on the Earth system.
\r\n\r\nFirst, we develop novel machine learning methods for hyperspectral radiative transfer simulations. Hyperspectral technique is one of the most popular and powerful methods for atmospheric remote sensing and is widely used for temperature, gas, aerosol, and cloud retrievals. However, accurate forward radiative transfer simulations are computationally expensive since they require a larger number of monochromatic radiative transfer calculations. We, therefore explore the feasibility of machine learning techniques for fast hyperspectral radiative transfer simulations that perform calculations at a small fraction of hyperspectral wavelengths and extend them across the entire spectral range. The machine learning-based approach achieves better performance than the traditional principal component analysis (PCA) method.
\r\n\r\nSecond, we evaluate modeled hyperspectral infrared spectra against satellite all-sky observations. The national weather centers obtain data from hyperspectral infrared sounders on a global scale. The cloudless scenario of this data is used to initialize weather forecasts, including temperature, water vapor, water cloud, and ice cloud profiles on a global grid. Although the data from these satellites are sensitive to the vertical distribution of ice and liquid water in the clouds, this information is not fully utilized. In this study, we evaluate how well the modeled spectra compare to AIRS observations using different cloud overlap models. We hope that this information can be used to verify clouds in the National Meteorological Center model and to initialize forecasts in the future.
\r\n\r\nIn the last chapter, we use radiation-based analytic approaches to study human impacts on the Earth system. In the first study case, we show that the radiative forcing due to geospatially redistributed anthropogenic aerosols mainly determined the spatial variations of winter extreme weather in the Northern Hemisphere during 1970-2005, which is a unique transition period for global aerosol forcing. In the second case, we review satellite and ground-based observations and conduct state-of-art atmospheric model simulations during the COVID-19 lockdown period. The halted human activities during the COVID-19 pandemic in China provided a unique experiment to assess the efficiency of air-pollution mitigation.
", "doi": "10.7907/1ck6-wx77", "publication_date": "2022", "thesis_type": "phd", "thesis_year": "2022" }, { "id": "thesis:11568", "collection": "thesis", "collection_id": "11568", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05302019-121137858", "primary_object_url": { "basename": "Ruan_thesis_final.pdf", "content": "final", "filesize": 9455377, "license": "other", "mime_type": "application/pdf", "url": "/11568/1/Ruan_thesis_final.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Oceanic Bottom Boundary Layers and Abyssal Overturning Circulation", "author": [ { "family_name": "Ruan", "given_name": "Xiaozhou", "orcid": "0000-0003-1240-1584", "clpid": "Ruan-Xiaozhou" } ], "thesis_advisor": [ { "family_name": "Thompson", "given_name": "Andrew F.", "clpid": "Thompson-A-F" } ], "thesis_committee": [ { "family_name": "Schneider", "given_name": "Tapio", "clpid": "Schneider-T" }, { "family_name": "Thompson", "given_name": "Andrew F.", "clpid": "Thompson-A-F" }, { "family_name": "Callies", "given_name": "Joern", "orcid": "0000-0002-6815-1230", "clpid": "Callies-J" }, { "family_name": "McKeon", "given_name": "Beverley J.", "clpid": "McKeon-B-J" }, { "family_name": "Stewart", "given_name": "Andrew L.", "clpid": "Stewart-A-L" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "The vast amount of carbon and heat exchange between the abyssal and upper ocean and subsequently the atmosphere is paced by the abyssal overturning circulation. A key component of the abyssal overturning circulation is the formation and consumption of the densest water mass on Earth, Antarctic Bottom Water (AABW), namely the conversion of North Atlantic Deep Water (NADW) to AABW and the consumption of AABW via small-scale diapycnal mixing. Yet, this pathway of AABW spanning thousands of kilometers has not been successfully reproduced in large-scale general circulation models (GCM). What is missing is essentially the understanding and resolution of small-scale physics involved in converting deep and bottom waters from one density class to another, the water mass transformation (WMT). In this thesis, we focus on small-scale (both in the horizontal and vertical directions) dynamics near the BBL, where enhanced shear, mixing and turbulence exist to facilitate effective WMT above the seafloor.
\r\n\r\nFrom high-resolution ocean glider observations around Antarctica, we find that a portion of Lower Circumpolar Deep Water, a branch of NADW, becomes lighter via mixing with light shelf water over the continental slope and shelf, instead of being converted into dense AABW under sea ice. This mixing is likely induced by submesoscale symmetric instability coming from a strong boundary current interacting with the sloping topography in the BBL. We then consider how to sustain the consumption of AABW in the global mid-ocean ridge system. Using numerical models, we show that submesoscale baroclinic eddies are crucial to maintaining strong stratification over the flanks of the mid-ocean ridges and thus permitting effective WMT. Lastly, we consider the interaction between external mean flows and stratified BBL over sloping topography. With the large-scale turbulence resolved in a large-eddy simulation model, we propose a new theoretical framework to describe the evolution of the BBL and the Eulerian advection of its associated stratification when external barotropic flows are present. This new framework can be used to parameterize bottom friction, important for closing the kinetic energy budget of the global ocean. We further extend this interaction to a horizontally-sheared and temporally-oscillating external mean flow and explore the response of the BBL and the BBL-interior mass exchange with simple turbulent parameterizations.
\r\n\r\nUsing a combination of different approaches, we confirm that the long-overlooked oceanic BBL is the key location for closing the abyssal overturning circulation. More importantly, without appropriate techniques to tackle the currently unresolved small-scale processes, they will likely remain a narrow bottleneck in understanding the abyssal overturning circulation.
", "doi": "10.7907/6EZA-R251", "publication_date": "2019", "thesis_type": "phd", "thesis_year": "2019" }, { "id": "thesis:11047", "collection": "thesis", "collection_id": "11047", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06082018-100127824", "primary_object_url": { "basename": "WEI-HO-HSUAN-2018.pdf", "content": "final", "filesize": 7812568, "license": "other", "mime_type": "application/pdf", "url": "/11047/1/WEI-HO-HSUAN-2018.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Dynamics of Seasonally-Varying Tropical Convergence Zones", "author": [ { "family_name": "Wei", "given_name": "Ho-Hsuan", "orcid": "0000-0002-6201-9810", "clpid": "Wei-Ho-Hsuan" } ], "thesis_advisor": [ { "family_name": "Bordoni", "given_name": "Simona", "orcid": "0000-0003-4771-3350", "clpid": "Bordoni-S" } ], "thesis_committee": [ { "family_name": "Thompson", "given_name": "Andrew F.", "orcid": "0000-0003-0322-4811", "clpid": "Thompson-A-F" }, { "family_name": "Ingersoll", "given_name": "Andrew P.", "orcid": "0000-0002-2035-9198", "clpid": "Ingersoll-A-P" }, { "family_name": "Schneider", "given_name": "Tapio", "orcid": "0000-0001-5687-2287", "clpid": "Schneider-T" }, { "family_name": "Teixeira", "given_name": "Joao", "clpid": "Teixeira-Joao" }, { "family_name": "Bordoni", "given_name": "Simona", "orcid": "0000-0003-4771-3350", "clpid": "Bordoni-S" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "In the tropics, rain tends to be organized along concentrated rain bands, with the Intertropical Convergence Zone (ITCZ) over the ocean and monsoonal convergence zones over tropical land masses being particularly prominent features affecting hundreds of millions of people. What fundamentally controls the spatial and temporal distribution of these tropical rainbands remains an outstanding question in the literature. This thesis aims to enhance our understanding of the dynamics of seasonally migrating convergence zones over the ocean and in the South Asian monsoon region.
\r\n \r\nFirst, we explore to what extent energetic arguments that have provided insight into the position and shifts of the annual and zonal mean ITCZ can also be applied on shorter timescales. Idealized aquaplanet simulations show that the energy flux equator (EFE) always leads the ITCZ, leading to a breakdown of the commonly assumed anti-correlation between the ITCZ position and the cross-equatorial energy transport. At times during which the EFE and the ITCZ reside on opposite sides of the equator, the required energy transport is in fact achieved by the Hadley cell, in which the ITCZ is embedded, changing its vertical structure into one of negative gross moist stability. One way in which this is accomplished is through the development of a shallow return flow at levels near minimum moist static energy. While the relationship between the EFE and the ITCZ in the observed seasonal cycle is more complex than what is seen in the idealized simulations, the development of bottom-heavy circulations is a common feature both in the zonal mean and in individual longitudinal sectors at times when the EFE and the ITCZ are in opposite hemispheres.
\r\n \r\nIn the last chapter of this thesis, we explore changes in the South Asian monsoon as topography over Africa is removed in the full-physics GFDL AM2.1 GCM. Against expectations, the removal of the African topography is accompanied by a strengthening of the precipitation over India despite a weakening of the Somali jet. This counter-intuitive precipitation increase is associated with the development of a lower-level cyclonic wind anomaly, and associated meridional moisture flux convergence, over the Indian peninsula. Potential vorticity (PV) budget analyses following air parcel trajectories show that this cyclonic anomaly arises because, in the absence of the blocking effect of the African topography, air particles that reach the Arabian Sea originate at higher latitude and hence have a higher background planetary vorticity.
", "doi": "10.7907/GAPR-QY60", "publication_date": "2018", "thesis_type": "phd", "thesis_year": "2018" }, { "id": "thesis:10989", "collection": "thesis", "collection_id": "10989", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05312018-154833107", "primary_object_url": { "basename": "caltech-thesis-zhang-xiyue-final.pdf", "content": "final", "filesize": 5643782, "license": "other", "mime_type": "application/pdf", "url": "/10989/2/caltech-thesis-zhang-xiyue-final.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "Dynamics of Resolved Polar Clouds", "author": [ { "family_name": "Zhang", "given_name": "Xiyue", "orcid": "0000-0002-6031-7830", "clpid": "Zhang-Xiyue" } ], "thesis_advisor": [ { "family_name": "Schneider", "given_name": "Tapio", "orcid": "0000-0001-5687-2287", "clpid": "Schneider-T" } ], "thesis_committee": [ { "family_name": "Bordoni", "given_name": "Simona", "orcid": "0000-0003-4771-3350", "clpid": "Bordoni-S" }, { "family_name": "Thompson", "given_name": "Andrew F.", "orcid": "0000-0003-0322-4811", "clpid": "Thompson-A-F" }, { "family_name": "Teixeira", "given_name": "Joao", "clpid": "Teixeira-Joao" }, { "family_name": "Seinfeld", "given_name": "John H.", "orcid": "0000-0003-1344-4068", "clpid": "Seinfeld-J-H" }, { "family_name": "Schneider", "given_name": "Tapio", "orcid": "0000-0001-5687-2287", "clpid": "Schneider-T" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "The polar regions have been experiencing rapid warming and ice loss as greenhouse gas concentrations have risen. The projected warming in the Arctic varies significantly across climate models, part of which is attributed to polar cloud feedbacks. This thesis addresses the question of what drives the changes in polar clouds as the climate warms, using a large eddy simulation (LES) model. LES is a powerful high-resolution model that resolves the most energetic turbulence relevant for clouds. First, we focus on the Arctic boundary layer clouds through three observation based case studies. The cloud and boundary layer characteristics simulated by the LES agree reasonably well with observations and model intercomparisons. We found that during polar night over sea ice, cloud water path increases with temperature and free-tropospheric relative humidity, but it decreases with inversion strength across the cloud top. Most of these changes can be explained by a mixed-layer model. The strength of the estimated positive cloud longwave feedback largely depends on the cloud top inversion strength. Next, we extend the LES domain to cover the entire polar troposphere, and use output from an idealized GCM as forcing to drive the LES. This novel framework allows changes in the large-scale circulation to be parameterized in the LES. The simulated seasonal cycle of liquid clouds resembles observations. In a warmer climate, there is a significant decrease of the low-level liquid clouds during summer and autumn. In spring and winter, liquid clouds increase at all levels. Both the liquid and ice cloud tops rise as the climate warms. Offline radiative transfer calculations estimate a positive cloud feedback that is dominated by longwave feedback.\r\n", "doi": "10.7907/69E7-0Q10", "publication_date": "2018", "thesis_type": "phd", "thesis_year": "2018" }, { "id": "thesis:10290", "collection": "thesis", "collection_id": "10290", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06052017-175613926", "primary_object_url": { "basename": "walker_jennifer_2017.pdf", "content": "final", "filesize": 11353719, "license": "other", "mime_type": "application/pdf", "url": "/10290/1/walker_jennifer_2017.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "Seasonal and Interannual Variability in South Asian Monsoon Dynamics", "author": [ { "family_name": "Walker", "given_name": "Jennifer Marie", "orcid": "0000-0002-1709-0888", "clpid": "Walker-Jennifer-Marie" } ], "thesis_advisor": [ { "family_name": "Bordoni", "given_name": "Simona", "clpid": "Bordoni-S" } ], "thesis_committee": [ { "family_name": "Thompson", "given_name": "Andrew F.", "clpid": "Thompson-A-F" }, { "family_name": "Bordoni", "given_name": "Simona", "clpid": "Bordoni-S" }, { "family_name": "Schneider", "given_name": "Tapio", "clpid": "Schneider-T" }, { "family_name": "Su", "given_name": "Hui", "clpid": "Su-Hui" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "Recent theoretical advances indicate that the South Asian summer monsoon (SASM) should be viewed as an energetically-direct cross-equatorial Hadley circulation, with the monsoonal precipitation primarily occurring in its ascending branch, rather than its traditional interpretation as a large land-sea breeze circulation. Despite these developments, very few studies have explored the implications of these emerging theories for the observed variability of the SASM.
\r\n\r\nThis is the goal of this PhD thesis, which uses atmospheric reanalysis data from recent decades to investigate seasonal transitions and interannual variability of the SASM. Our approach differs from previous studies in its focus on the large-scale atmospheric dynamics of the SASM: more specifically, we analyze the tropical circulation throughout the SASM sector and its relationship with extratropical weather systems in both hemispheres that can affect transports of momentum and energy.
\r\n\r\nThe atmospheric moisture budget over the SASM region provides a crucial starting point for our work. We use this budget to introduce a novel objective index for the onset and retreat of the SASM, which robustly captures the expected seasonal transitions in precipitation and winds and eliminates the need for arbitrarily selected thresholds. Using this index, we show how the SASM onset and retreat are associated with a coherent set of seasonal transitions in circulation, jet streams, precipitation, energetics, and momentum balance throughout the SASM sector. These transitions closely resemble those of the zonal mean Hadley circulation, indicating that the SASM projects strongly onto the zonal mean and that the observed SASM is consistent with new theoretical interpretations.
\r\n\r\nWe also use the atmospheric moisture budget to define a new index for the SASM strength on interannual time scales. We show that interannual variability in SASM net precipitation is primarily caused by variations in winds rather than variations in humidity, highlighting the importance of understanding drivers of the large-scale circulation and its changes. We then use linear regression analysis to identify robust changes in the circulation associated with SASM year-to-year variability. We find that strong monsoons are associated with a northward expansion of the overturning circulation and a decreased near-surface land-sea thermal contrast, in disagreement with the traditional view of the SASM as a sea-breeze circulation. We also find teleconnections between SASM strength and temperatures, winds, and momentum and energy transports in the southern hemisphere extratropics. These interhemispheric teleconnections, which have not been previously identified, suggest new directions for future research to improve our understanding of the mechanisms involved in SASM variability.
\r\n\r\nImportant advances in modeling and predicting the SASM at all timescales require a deeper understanding of the fundamental processes driving this system. Through theoretically-guided analyses of the SASM observed variability, this dissertation work takes an important step in this direction and provides novel insight into long-standing open questions on the SASM, with crucial implications for its predictability.
\r\n", "doi": "10.7907/Z9513W8K", "publication_date": "2017", "thesis_type": "phd", "thesis_year": "2017" }, { "id": "thesis:9981", "collection": "thesis", "collection_id": "9981", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:11122016-111133209", "type": "thesis", "title": "Dynamics of the Intertropical Convergence Zone", "author": [ { "family_name": "Bischoff", "given_name": "Tobias", "orcid": "0000-0003-3930-2762", "clpid": "Bischoff-Tobias" } ], "thesis_advisor": [ { "family_name": "Schneider", "given_name": "Tapio", "clpid": "Schneider-T" } ], "thesis_committee": [ { "family_name": "Thompson", "given_name": "Frederick B.", "clpid": "Thompson-F-B" }, { "family_name": "Schneider", "given_name": "Tapio", "clpid": "Schneider-T" }, { "family_name": "Bordoni", "given_name": "Simona", "clpid": "Bordoni-S" }, { "family_name": "Adkins", "given_name": "Jess F.", "clpid": "Adkins-J-F" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "Previous studies have shown that the latitude of the Intertropical Convergence Zone (ITCZ) is negatively correlated with cross-equatorial atmospheric energy transport and that the ITCZ shifts southward as the northern hemisphere cools and the northward cross-equatorial energy transport strengthens. However, it has remained unclear what controls the sensitivity of the ITCZ position to cross-equatorial energy transport, and what other factors may lead to shifts of the ITCZ position. In this thesis, it is shown how an energetic perspective using the vertically-integrated moist static energy balance of the atmosphere can be used to address this question. Climate states with a double-ITCZ around the equator also occur, for example, seasonally over the eastern Pacific, and frequently in climate models. Here it is shown how the ITCZ position is connected to the energy balance near the equator under a wide range of circumstances, including states with single and double ITCZs and using a Taylor expansion of the meridional energy transport around the equator quantitative estimates for the ITCZ location are derived. Simulations with an idealized aquaplanet general circulation model (GCM) confirm the quantitative adequacy of these relations. Using these ideas, an idealized precipitation model for the tropics is presented that is able to capture variations of paleoclimatological precipitation records on orbital time scales. The results provide a framework for assessing and understanding causes of common climate model biases and for interpreting tropical precipitation changes, such as those evident in records of climates of the past.", "doi": "10.7907/Z97M05XR", "publication_date": "2017", "thesis_type": "phd", "thesis_year": "2017" }, { "id": "thesis:9536", "collection": "thesis", "collection_id": "9536", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:01202016-022601840", "primary_object_url": { "basename": "wills_robert_thesis_2016.pdf", "content": "final", "filesize": 44989292, "license": "other", "mime_type": "application/pdf", "url": "/9536/1/wills_robert_thesis_2016.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Stationary Eddies and Zonal Variations of the Global Hydrological Cycle in a Changing Climate", "author": [ { "family_name": "Wills", "given_name": "Robert Christopher", "clpid": "Wills-Robert-Christopher" } ], "thesis_advisor": [ { "family_name": "Schneider", "given_name": "Tapio", "clpid": "Schneider-T" } ], "thesis_committee": [ { "family_name": "Thompson", "given_name": "Andrew F.", "clpid": "Thompson-A-F" }, { "family_name": "Bordoni", "given_name": "Simona", "clpid": "Bordoni-S" }, { "family_name": "Adkins", "given_name": "Jess F.", "clpid": "Adkins-J-F" }, { "family_name": "Lamb", "given_name": "Michael P.", "clpid": "Lamb-M-P" }, { "family_name": "Schneider", "given_name": "Tapio", "clpid": "Schneider-T" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "This thesis advances our physical understanding of the sensitivity of the hydrological cycle to global warming. Specifically, it focuses on changes in the longitudinal (zonal) variation of precipitation minus evaporation (P - E), which is predominantly controlled by planetary-scale stationary eddies. By studying idealized general circulation model (GCM) experiments with zonally varying boundary conditions, this thesis examines the mechanisms controlling the strength of stationary-eddy circulations and their role in the hydrological cycle. The overarching goal of this research is to understand the cause of changes in regional P - E with global warming. An understanding of such changes can be useful for impact studies focusing on water availability, ecosystem management, and flood risk.
\r\n\r\nBased on a moisture-budget analysis of ERA-Interim data, we establish an approximation for zonally anomalous P - E in terms of surface moisture content and stationary-eddy vertical motion in the lower troposphere. Part of the success of this approximation comes from our finding that transient-eddy moisture fluxes partially cancel the effect of stationary-eddy moisture advection, allowing divergent circulations to dominate the moisture budget. The lower-tropospheric vertical motion is related to horizontal motion in stationary eddies by Sverdrup and Ekman balance. These moisture- and vorticity-budget balances also hold in idealized and comprehensive GCM simulations across a range of climates.
\r\n\r\nBy examining climate changes in the idealized and comprehensive GCM simulations, we are able to show the utility of the vertical motion P - E approximation for splitting changes in zonally anomalous P - E into thermodynamic and dynamic components. Shifts in divergent stationary-eddy circulations dominate changes in zonally anomalous P - E. This limits the local utility of the \"wet gets wetter, dry gets drier\u201d idea, where existing P - E patterns are amplified with warming by the increase in atmospheric moisture content, with atmospheric circulations held fixed. The increase in atmospheric moisture content manifests instead in an increase in the amplitude of the zonally anomalous hydrological cycle as measured by the zonal variance of P - E. However, dynamic changes, particularly the slowdown of divergent stationary-eddy circulations, limit the strengthening of the zonally anomalous hydrological cycle. In certain idealized cases, dynamic changes are even strong enough to reverse the tendency towards \"wet gets wetter, dry gets drier\u201d with warming.
\r\n\r\nMotivated by the importance of stationary-eddy vertical velocities in the moisture budget analysis, we examine controls on the amplitude of stationary eddies across a wide range of climates in an idealized GCM with simple topographic and ocean-heating zonal asymmetries. An analysis of the thermodynamic equation in the vicinity of topographic forcing reveals the importance of on-slope surface winds, the midlatitude isentropic slope, and latent heating in setting the amplitude of stationary waves. The response of stationary eddies to climate change is determined primarily by the strength of zonal surface winds hitting the mountain. The sensitivity of stationary-eddies to this surface forcing increases with climate change as the slope of midlatitude isentropes decreases. However, latent heating also plays an important role in damping the stationary-eddy response, and this damping becomes stronger with warming as the atmospheric moisture content increases. We find that the response of tropical overturning circulations forced by ocean heat-flux convergence is described by changes in the vertical structure of moist static energy and deep convection. This is used to derive simple scalings for the Walker circulation strength that capture the monotonic decrease with warming found in our idealized simulations.
\r\n\r\nThrough the work of this thesis, the advances made in understanding the amplitude of stationary-waves in a changing climate can be directly applied to better understand and predict changes in the zonally anomalous hydrological cycle.
", "doi": "10.7907/Z91V5BX8", "publication_date": "2016", "thesis_type": "phd", "thesis_year": "2016" }, { "id": "thesis:9037", "collection": "thesis", "collection_id": "9037", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06252015-185841054", "type": "thesis", "title": "Observations and Modeling of Tropical Planetary Atmospheres", "author": [ { "family_name": "Laraia", "given_name": "Anne Louise", "clpid": "Laraia-Anne-Louise" } ], "thesis_advisor": [ { "family_name": "Bordoni", "given_name": "Simona", "clpid": "Bordoni-S" } ], "thesis_committee": [ { "family_name": "Wennberg", "given_name": "Paul O.", "clpid": "Wennberg-P-O" }, { "family_name": "Schneider", "given_name": "Tapio", "clpid": "Schneider-T" }, { "family_name": "Ingersoll", "given_name": "Andrew P.", "clpid": "Ingersoll-A-P" }, { "family_name": "Thompson", "given_name": "Andrew F.", "clpid": "Thompson-A-F" }, { "family_name": "Bordoni", "given_name": "Simona", "clpid": "Bordoni-S" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "This thesis is a comprised of three different projects within the topic of tropical atmospheric dynamics. First, I analyze observations of thermal radiation from Saturn\u2019s atmosphere and from them, determine the latitudinal distribution of ammonia vapor near the 1.5-bar pressure level. The most prominent feature of the observations is the high brightness temperature of Saturn\u2019s subtropical latitudes on either side of the equator. After comparing the observations to a microwave radiative transfer model, I find that these subtropical bands require very low ammonia relative humidity below the ammonia cloud layer in order to achieve the high brightness temperatures observed. We suggest that these bright subtropical bands represent dry zones created by a meridionally overturning circulation.
\r\n\r\nSecond, I use a dry atmospheric general circulation model to study equatorial superrotation in terrestrial atmospheres. A wide range of atmospheres are simulated by varying three parameters: the pole-equator radiative equilibrium temperature contrast, the convective lapse rate, and the planetary rotation rate. A scaling theory is developed that establishes conditions under which superrotation occurs in terrestrial atmospheres. The scaling arguments show that superrotation is favored when the off-equatorial baroclinicity and planetary rotation rates are low. Similarly, superrotation is favored when the convective heating strengthens, which may account for the superrotation seen in extreme global-warming simulations.
\r\n\r\nThird, I use a moist slab-ocean general circulation model to study the impact of a zonally-symmetric continent on the distribution of monsoonal precipitation. I show that adding a hemispheric asymmetry in surface heat capacity is sufficient to cause symmetry breaking in both the spatial and temporal distribution of precipitation. This spatial symmetry breaking can be understood from a large-scale energetic perspective, while the temporal symmetry breaking requires consideration of the dynamical response to the heat capacity asymmetry and the seasonal cycle of insolation. Interestingly, the idealized monsoonal precipitation bears resemblance to precipitation in the Indian monsoon sector, suggesting that this work may provide insight into the causes of the temporally asymmetric distribution of precipitation over southeast Asia.
\r\n", "doi": "10.7907/Z9J1012T", "publication_date": "2016", "thesis_type": "phd", "thesis_year": "2016" }, { "id": "thesis:9107", "collection": "thesis", "collection_id": "9107", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:08192015-043550928", "type": "thesis", "title": "Simulations and Mechanisms of Subtropical Low-cloud Response to Climate Change", "author": [ { "family_name": "Tan", "given_name": "Zhihong", "orcid": "0000-0002-7422-3317", "clpid": "Tan-Zhihong" } ], "thesis_advisor": [ { "family_name": "Schneider", "given_name": "Tapio", "orcid": "0000-0001-5687-2287", "clpid": "Schneider-T" }, { "family_name": "Teixeira", "given_name": "Joao", "clpid": "Teixeira-J" } ], "thesis_committee": [ { "family_name": "Seinfeld", "given_name": "John H.", "orcid": "0000-0003-1344-4068", "clpid": "Seinfeld-J-H" }, { "family_name": "Schneider", "given_name": "Tapio", "orcid": "0000-0001-5687-2287", "clpid": "Schneider-T" }, { "family_name": "Teixeira", "given_name": "Joao", "clpid": "Teixeira-Joao" }, { "family_name": "Bordoni", "given_name": "Simona", "orcid": "0000-0003-4771-3350", "clpid": "Bordoni-S" }, { "family_name": "Wennberg", "given_name": "Paul O.", "orcid": "0000-0002-6126-3854", "clpid": "Wennberg-P-O" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "This thesis focuses on improving the simulation skills and the theoretical understanding of the subtropical low cloud response to climate change.
\r\n\r\nFirst, an energetically consistent forcing framework is designed and implemented for the large eddy simulation (LES) of the low-cloud response to climate change. The three representative current-day subtropical low cloud regimes of cumulus (Cu), cumulus-over-stratocumulus, and stratocumulus (Sc) are all well simulated with this framework, and results are comparable to the conventional fixed-SST approach. However, the cumulus response to climate warming subject to energetic constraints differs significantly from the conventional approach with fixed SST. Under the energetic constraint, the subtropics warm less than the tropics, since longwave (LW) cooling is more efficient with the drier subtropical free troposphere. The surface latent heat flux (LHF) also increases only weakly subject to the surface energetic constraint. Both factors contribute to an increased estimated inversion strength (EIS), and decreased inversion height. The decreased Cu-depth contributes to a decrease of liquid water path (LWP) and weak positive cloud feedback. The conventional fixed-SST approach instead simulates a strong increase in LHF and deepening of the Cu layer, leading to a weakly negative cloud feedback. This illustrates the importance of energetic constraints to the simulation and understanding of the sign and magnitude of low-cloud feedback.
\r\n\r\nSecond, an extended eddy-diffusivity mass-flux (EDMF) closure for the unified representation of sub-grid scale (SGS) turbulence and convection processes in general circulation models (GCM) is presented. The inclusion of prognostic terms and the elimination of the infinitesimal updraft fraction assumption makes it more flexible for implementation in models across different scales. This framework can be consistently extended to formulate multiple updrafts and downdrafts, as well as variances and covariances. It has been verified with LES in different boundary layer regimes in the current climate, and further development and implementation of this closure may help to improve our simulation skills and understanding of low-cloud feedback through GCMs.
", "doi": "10.7907/Z9JS9NC9", "publication_date": "2016", "thesis_type": "phd", "thesis_year": "2016" }, { "id": "thesis:8854", "collection": "thesis", "collection_id": "8854", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05112015-075223217", "primary_object_url": { "basename": "mbengue_cheikh_2015_thesis.pdf", "content": "final", "filesize": 3849313, "license": "other", "mime_type": "application/pdf", "url": "/8854/1/mbengue_cheikh_2015_thesis.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Storm Track Response to Perturbations in Climate", "author": [ { "family_name": "Mbengue", "given_name": "Cheikh Oumar", "clpid": "Mbengue-Cheikh-Oumar" } ], "thesis_advisor": [ { "family_name": "Schneider", "given_name": "Tapio", "orcid": "0000-0001-5687-2287", "clpid": "Schneider-T" } ], "thesis_committee": [ { "family_name": "Meiron", "given_name": "Daniel I.", "orcid": "0000-0003-0397-3775", "clpid": "Meiron-D-I" }, { "family_name": "McKeon", "given_name": "Beverley J.", "orcid": "0000-0003-4220-1583", "clpid": "McKeon-B-J" }, { "family_name": "Ravichandran", "given_name": "Guruswami", "orcid": "0000-0002-2912-0001", "clpid": "Ravichandran-G" }, { "family_name": "Teixeira", "given_name": "Joao", "clpid": "Teixeira-Joao" }, { "family_name": "Schneider", "given_name": "Tapio", "orcid": "0000-0001-5687-2287", "clpid": "Schneider-T" } ], "local_group": [ { "literal": "GALCIT" }, { "literal": "div_eng" } ], "abstract": "This thesis advances our understanding of midlatitude storm tracks and how they respond to perturbations in the climate system. The midlatitude storm tracks are regions of maximal turbulent kinetic energy in the atmosphere. Through them, the bulk of the atmospheric transport of energy, water vapor, and angular momentum occurs in midlatitudes. Therefore, they are important regulators of climate, controlling basic features such as the distribution of surface temperatures, precipitation, and winds in midlatitudes. Storm tracks are robustly projected to shift poleward in global-warming simulations with current climate models. Yet the reasons for this shift have remained unclear. Here we show that this shift occurs even in extremely idealized (but still three-dimensional) simulations of dry atmospheres. We use these simulations to develop an understanding of the processes responsible for the shift and develop a conceptual model that accounts for it.
\r\n\r\nWe demonstrate that changes in the convective static stability in the deep tropics alone can drive remote shifts in the midlatitude storm tracks. Through simulations with a dry idealized general circulation model (GCM), midlatitude storm tracks are shown to be located where the mean available potential energy (MAPE, a measure of the potential energy available to be converted into kinetic energy) is maximal. As the climate varies, even if only driven by tropical static stability changes, the MAPE maximum shifts primarily because of shifts of the maximum of near-surface meridional temperature gradients. The temperature gradients shift in response to changes in the width of the tropical Hadley circulation, whose width is affected by the tropical static stability. Storm tracks generally shift in tandem with shifts of the subtropical terminus of the Hadley circulation.
\r\n\r\nWe develop a one-dimensional diffusive energy-balance model that links changes in the Hadley circulation to midlatitude temperature gradients and so to the storm tracks. It is the first conceptual model to incorporate a dynamical coupling between the tropical Hadley circulation and midlatitude turbulent energy transport. Numerical and analytical solutions of the model elucidate the circumstances of when and how the storm tracks shift in tandem with the terminus of the Hadley circulation. They illustrate how an increase of only the convective static stability in the deep tropics can lead to an expansion of the Hadley circulation and a poleward shift of storm tracks.
\r\n\r\nThe simulations with the idealized GCM and the conceptual energy-balance model demonstrate a clear link between Hadley circulation dynamics and midlatitude storm track position. With the help of the hierarchy of models presented in this thesis, we obtain a closed theory of storm track shifts in dry climates. The relevance of this theory for more realistic moist climates is discussed.
", "doi": "10.7907/Z9FT8J05", "publication_date": "2015", "thesis_type": "phd", "thesis_year": "2015" }, { "id": "thesis:7309", "collection": "thesis", "collection_id": "7309", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:12062012-130125923", "primary_object_url": { "basename": "levine_xavier_2013_thesis.pdf", "content": "final", "filesize": 2544446, "license": "other", "mime_type": "application/pdf", "url": "/7309/1/levine_xavier_2013_thesis.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "Dynamics of Earth's Hadley Circulation", "author": [ { "family_name": "Levine", "given_name": "Xavier Josselin", "clpid": "Levine-Xavier-Josselin" } ], "thesis_advisor": [ { "family_name": "Schneider", "given_name": "Tapio", "clpid": "Schneider-T" } ], "thesis_committee": [ { "family_name": "Bordoni", "given_name": "Simona", "clpid": "Bordoni-S" }, { "family_name": "Ingersoll", "given_name": "Andrew P.", "clpid": "Ingersoll-A-P" }, { "family_name": "Schneider", "given_name": "Tapio", "clpid": "Schneider-T" }, { "family_name": "Wennberg", "given_name": "Paul O.", "clpid": "Wennberg-P-O" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "This thesis advances our understanding of the mechanisms controlling the Hadley circulation, and its interaction with eddies on planetary scales in particular. On Earth, and more generally in a rapidly rotating and differentially heated planet, planetary scale eddies in the extratropics interact with the mean flow in the tropics, contributing to the driving of the Hadley circulation. A hierarchy of numerical models is used to simulate and understand the relative importance of eddies in the driving of the Hadley circulation. In a global warming experiment, the Hadley circulation is found to strengthen in colder climates and weaken in warmer climates, with a maximum strength in a climate close to present-day Earth\u2019s. This nonmonotonicity is shown to be consistent with variations in the eddy activity in the midlatitudes. The cells are also found to widen over the entire range of this climate change. A criterion quantifying the importance of baroclinic waves in setting the depth of the troposphere, which is modified to account for the effect of convective adjustment on planetary Rossby waves activity, is used to explain the shifts in the terminus of the Hadley circulation for a wide range of climate scenarios. Additionally, by comparing simulations with and without ocean heat transport, it is shown that accounting for low-latitude ocean heat transport and its coupling to wind stress is essential to obtain Hadley circulations in a dynamical regime resembling Earth\u2019s. These changes in the strength and extent are found to be captured in a simple one-dimensional model that relies on standard assumptions about the thermodynamic properties of the atmosphere in the low-latitude regions and with a simple representation of eddy fluxes. Further work with this model, which may be amenable to analytical progress, could provide a quantitative understanding for the sensitivity of the Hadley circulation in comprehensive GCM simulations of 21st century global warming scenarios.
", "doi": "10.7907/Z25V-TA20", "publication_date": "2013", "thesis_type": "phd", "thesis_year": "2013" }, { "id": "thesis:6880", "collection": "thesis", "collection_id": "6880", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:03292012-204204319", "primary_object_url": { "basename": "thesismain.pdf", "content": "final", "filesize": 12051492, "license": "other", "mime_type": "application/pdf", "url": "/6880/1/thesismain.pdf", "version": "v7.0.0" }, "type": "thesis", "title": "Computational Modeling Studies of Fundamental Aerosol-Cloud Interactions", "author": [ { "family_name": "Lebo", "given_name": "Zachary John", "clpid": "Lebo-Zachary-John" } ], "thesis_advisor": [ { "family_name": "Seinfeld", "given_name": "John H.", "clpid": "Seinfeld-J-H" } ], "thesis_committee": [ { "family_name": "Schneider", "given_name": "Tapio", "clpid": "Schneider-T" }, { "family_name": "Ingersoll", "given_name": "Andrew P.", "clpid": "Ingersoll-A-P" }, { "family_name": "Li", "given_name": "Juilin F.", "clpid": "Li-J-F" }, { "family_name": "Seinfeld", "given_name": "John H.", "clpid": "Seinfeld-J-H" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "Basic questions regarding the interaction between changes in human activity and the atmosphere remain unanswered. Among these, the link between aerosol particles and cloud formation and development, especially in an altered climate, is a large point of uncertainty in recent climate projections. This should come as no surprise given the uncertainty in model parameters required to predict droplet activation, even in the most detailed models used for climate predictions. Here, a detailed spectral mixed-phase microphysics scheme and a state-of-the-art continuous two-dimensional (2-D) aerosol-droplet microphysics scheme have been developed and coupled to the Weather Research and Forecasting (WRF) model to more closely analyze the effects of aerosol perturbations on single clouds or cloud systems with the hope of ultimately improving numerical parameterizations used by microphysics schemes in general circulation models (GCMs).
\r\n\r\nThe continuous 2-D aerosol-droplet model is developed to explicitly treat the entire spectrum of aerosol, haze droplets, cloud droplets, and drizzle drops while allowing the solute mass spectrum to evolve within the droplets. In other words, the aerosol mass is conserved and regeneration of aerosol particles upon droplet evaporation is physically accurate without any a priori assumptions. The model is tested by performing simulations of marine stratocumulus and the results are compared with those from the aforementioned bin and bulk models. It is shown that microphysical processing of aerosols alone results in a large shift in the aerosol spectrum toward larger particles (via collision-coalescence of droplets). This could have potentially large effects on the activation of regenerated particles. Future studies with the model will address the need for better parameterizations of the aerosol regeneration process.
\r\n\r\nThe spectral mixed-phase microphysics scheme is used in conjunction with a two-moment bulk microphysics model to study the effect of aerosol perturbations on deep convective clouds. The bin model shows that with an increase in aerosol number concentration comes an invigoration and a decrease in precipitation. On the other hand, the bulk model suggests that the storm ought to weaken and precipitation will increase in a more polluted environment. The invigoration predicted by the bin model is a result of the suppression of the collision-coalescence process that permits more droplets to be lofted above the freezing level, hence increasing the bulk freezing rate aloft. The additional freezing and subsequent deposition acts to increase the latent heating and thus increase buoyancy. However, the cloud particles in the polluted cases are now smaller and more numerous and consequently have a shorter evaporation/sublimation timescale and a longer sedimentation time-scale. The ultimate result is for precipitation to decrease in conjunction with a moistening of the mid- to upper-troposphere. The difference in the sign of the aerosol effect between the two models is thought to be related to the saturation adjustment scheme used in the bulk model and is addressed by including an explicit treatment of condensation and activation within the bulk model, similar to the algorithm utilized in the bin model. The results of the inter-model comparison demonstrate the significance of the saturation adjustment assumption on the sign and magnitude of the aerosol effect on deep convective clouds.
", "doi": "10.7907/HH11-8N22", "publication_date": "2012", "thesis_type": "phd", "thesis_year": "2012" }, { "id": "thesis:6533", "collection": "thesis", "collection_id": "6533", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:07012011-191902511", "type": "thesis", "title": "The General Circulation of the Tropical Atmosphere and Climate Changes", "author": [ { "family_name": "Merlis", "given_name": "Timothy Moore", "clpid": "Merlis-Timothy-Moore" } ], "thesis_advisor": [ { "family_name": "Schneider", "given_name": "Tapio", "clpid": "Schneider-T" } ], "thesis_committee": [ { "family_name": "Ingersoll", "given_name": "Andrew P.", "clpid": "Ingersoll-A-P" }, { "family_name": "Adkins", "given_name": "Jess F.", "clpid": "Adkins-J-F" }, { "family_name": "Bordoni", "given_name": "Simona", "clpid": "Bordoni-S" }, { "family_name": "Schneider", "given_name": "Tapio", "clpid": "Schneider-T" }, { "family_name": "Thompson", "given_name": "Andrew F.", "clpid": "Thompson-A-F" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "I examine the general circulation of the tropical atmosphere and climate changes. First, the response of the zonal surface temperature gradients and zonally asymmetric tropical overturning circulations (Walker circulations) to substantial changes in the longwave optical depth of the atmosphere in an idealized general circulation model (GCM) is compared with scaling theories. Second, the response of the hydrological cycle and monsoonal Hadley circulations to changes in top-of-atmosphere insolation associated with orbital precession is examined in an idealized GCM.
\r\n\r\nZonal surface temperature gradients and Walker circulations are examined over a wide range of climates simulated by varying the optical thickness in an idealized atmospheric GCM with a climate-invariant zonally asymmetric ocean energy flux. The tropical zonal surface temperature gradient and Walker circulation generally decrease as the climate warms in the GCM simulations. A scaling relationship based on a two-term balance in the surface energy budget accounts for the changes in the zonally asymmetric component of the GCM-simulated surface temperature gradients. A scaling estimate for the Walker circulation based on differential changes (precipitation rates and saturation specific humidity) in the hydrological cycle accounts for the GCM simulations provided locally averaged quantities are used in the estimate.
\r\n\r\nThe results of atmospheric GCM simulations with varied top-of-atmosphere insolation are analyzed to constrain orbitally-forced changes in the tropical atmospheric circulations and precipitation. When the perihelion is varied between solstices, there is more annual-mean precipitation in the hemisphere in which perihelion occurs during the summer solstice. In aquaplanet simulations, this is primarily associated with thermodynamic changes: there is a correlation between the seasonal cycle of the perturbed water vapor and the seasonal cycle of the Hadley circulation convergence. The monsoonal Hadley circulation does not respond to insolation gradients in a simple manner, as the atmosphere\u2019s energy stratification changes. An idealized continent that has a simple treatment of land surface hydrology and inhomogeneous heat capacity allows an assessment of how land-sea contrasts can mediate the response to orbital precession. In these simulations, the response of precipitation to orbital precession depends on changes in the atmospheric circulation, which strengthens when perihelion occurs in the summer of the hemisphere with the land region. The changes in atmospheric circulation are related to changes in both the top-of-atmosphere energy balance and the thermodynamic properties of the surface.
", "doi": "10.7907/DH11-0926", "publication_date": "2012", "thesis_type": "phd", "thesis_year": "2012" }, { "id": "thesis:6778", "collection": "thesis", "collection_id": "6778", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:01252012-143955675", "primary_object_url": { "basename": "soto_thesis.pdf", "content": "final", "filesize": 13198117, "license": "cc_by_nc_nd", "mime_type": "application/pdf", "url": "/6778/1/soto_thesis.pdf", "version": "v6.0.0" }, "type": "thesis", "title": "Dynamical Paleoclimatology of Mars", "author": [ { "family_name": "Soto", "given_name": "Alejandro", "clpid": "Soto-Alejandro" } ], "thesis_advisor": [ { "family_name": "Schneider", "given_name": "Tapio", "clpid": "Schneider-T" } ], "thesis_committee": [ { "family_name": "Ingersoll", "given_name": "Andrew P.", "clpid": "Ingersoll-A-P" }, { "family_name": "Schneider", "given_name": "Tapio", "clpid": "Schneider-T" }, { "family_name": "Ehlmann", "given_name": "Bethany L.", "clpid": "Ehlmann-B-L" }, { "family_name": "Bordoni", "given_name": "Simona", "clpid": "Bordoni-S" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "We investigated the dynamical paleoclimatology of Mars with a focus on three areas: large scale dynamics, atmospheric collapse, and controls on precipitation and aridity of a warm, wet Mars. We explored the changes, and lack of changes, in the large scale circulation over a range of atmospheric masses. We present the results here, with an emphasis on the response of the winds and the meridional transport.
\r\n\r\nThe conditions for continuous condensation of the CO2 atmospheres in the polar regions, often called 'atmospheric collapse', were explored by simulating the Martian atmosphere over a wide range of obliquities for a wide range of atmospheric thicknesses. As expected, atmospheric collapse occurs at low obliquities, but surprisingly, collapse occurs for high obliquities (up to 40\u25e6) for moderate atmospheric thicknesses (100's of millibars up to 1000 millibars). Using the MarsWRF model, we show that a competition between atmospheric heating feedbacks, including the greenhouse feedback and the heat transport feedback, and the condensation temperature feedback determines whether atmosphere collapse occurs.
\r\n\r\nFinally, we explored the precipitation and aridity of a warm, wet Mars with an active hydrological system. Even an extremely wet climate with a northern hemisphere ocean produces an extremely dry, desert climate in the southern hemisphere, with an equatorial band of rain and run off. Cross-equatorial flows deliver moist air from the northern ocean into the southern region, but topography and the distribution of land versus ocean limit the extent of the rainfall.
", "doi": "10.7907/3D9Y-DC44", "publication_date": "2012", "thesis_type": "phd", "thesis_year": "2012" }, { "id": "thesis:6479", "collection": "thesis", "collection_id": "6479", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05312011-112642236", "type": "thesis", "title": "Constraints on the Global Carbon Budget from Variations in Total Column Carbon Dioxide", "author": [ { "family_name": "Keppel-Aleks", "given_name": "Gretchen", "clpid": "Keppel-Aleks-Gretchen" } ], "thesis_advisor": [ { "family_name": "Wennberg", "given_name": "Paul O.", "clpid": "Wennberg-P-O" } ], "thesis_committee": [ { "family_name": "Schneider", "given_name": "Tapio", "clpid": "Schneider-T" }, { "family_name": "Wennberg", "given_name": "Paul O.", "clpid": "Wennberg-P-O" }, { "family_name": "Toon", "given_name": "Geoffrey C.", "clpid": "Toon-G-C" }, { "family_name": "Bordoni", "given_name": "Simona", "clpid": "Bordoni-S" }, { "family_name": "Yung", "given_name": "Yuk L.", "clpid": "Yung-Y-L" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Diagnosing the patterns and trends in the flux of carbon dioxide, CO\u2082, between the land or ocean and the atmosphere is necessary to predict the response of the carbon cycle to climate change. Atmospheric observations of the vertically averaged mixing ratio of CO\u2082, (CO\u2082), provide a new tool that complements existing observations of boundary layer CO\u2082 in constraining surface fluxes of CO2. My dissertation explores how variations in (CO\u2082) arise and how these variations can be used to estimate surface fluxes.
\r\n\r\nThis thesis takes advantage of (CO\u2082) measurements from the Total Carbon Column Observing Network (TCCON). This global network uses ground-based Fourier transform spectrometers to obtain direct solar spectra in the near infrared, from which (CO\u2082) is retrieved. Because variations in atmospheric CO\u2082 are relatively small, it is essential that the data achieve high precision and accuracy to be useful for carbon cycle science. Using a retrieval algorithm I developed to remove transient interference from clouds and aerosols, precise measurements are achievable under a range\r\nof meteorological conditions, allowing the inclusion of data from partially cloudy days.
\r\n\r\nAt midlatitude TCCON sites, (CO\u2082) varies substantially on diurnal, synoptic, and seasonal timescales. A comparison of diurnal variations in (CO\u2082) with flux tower observations of net ecosystem exchange in northern Wisconsin suggests that local ecosystem fluxes account for only 10%\u201315% of variation in (CO\u2082) on hourly timescales. I use an atmospheric transport model with imposed surface fluxes of CO\u2082 to examine further the sensitivity of (CO\u2082) to surface fluxes and find that, as in the observations, simulated (CO\u2082) is relatively insensitive to local phenomena. Large variations in local fluxes and local physics (e.g., convection) produce only small changes in atmospheric (CO\u2082) patterns. Patterns in (CO\u2082) are most sensitive to the large-scale north\u2013south flux gradient, as zonal variations in fluxes are smoothed by transport and therefore have little impact on the total column.
\r\n\r\nRapid temporal variations in midlatitude (CO\u2082) arise due to transport across north-south gradients, and can be used to infer information about large-scale spatial patterns in CO\u2082. Here, I use the correlation between synoptic-scale variations in (CO\u2082) and dynamical tracers, such as potential\r\ntemperature, to infer spatial gradients in large-scale (CO\u2082) from sparse ground-based data. These estimated gradients, as well as the amplitude of the seasonal cycle in (CO\u2082), can be used as diagnostics to evaluate flux models. In simulations with one such model, the Carnegie Ames Stanford\r\nApproach (CASA) ecosystem fluxes, gradients inferred from TCCON data are 75% larger than simulated CO\u2082 gradients during summer, while the seasonal cycle amplitudes in (CO\u2082) at midlatitude TCCON sites are between 20% and 40% larger than in simulations. Given that (CO\u2082) is insensitive to local fluxes, the mismatch between observations and simulations points to an underestimation of northern hemisphere ecosystem fluxes. Simulated (CO\u2082) diagnostics are consistent with TCCON data if boreal net ecosystem exchange is increased by 40%, a finding that suggests boreal ecosystem parameterizations must be reevaluated.
\r\n\r\nThis work demonstrates that variability in (CO\u2082) is driven by large-scale phenomena rather than local fluxes, and has important implications for interpreting (CO\u2082) measurements from satellites such as GOSAT and OCO-2. These results suggest that total column measurements will provide a strong constraint on large-scale flux estimates. At the same time, extracting information about regional fluxes from (CO\u2082) observations alone will be challenging. Coupling column and surface CO\u2082 observations will yield improved flux estimates as surface CO\u2082 observations will constrain regional flux patterns, superimposed on top of the large-scale flux distribution revealed by total column observations.
\r\n\r\n", "doi": "10.7907/5BZZ-BW98", "publication_date": "2011", "thesis_type": "phd", "thesis_year": "2011" }, { "id": "thesis:5838", "collection": "thesis", "collection_id": "5838", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05252010-172302796", "primary_object_url": { "basename": "thesis_kakani_2010_1.pdf", "content": "final", "filesize": 8795768, "license": "other", "mime_type": "application/pdf", "url": "/5838/1/thesis_kakani_2010_1.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "Effect of In Situ Animal-Fluid Interactions on Transport and Mixing", "author": [ { "family_name": "Young", "given_name": "Kakani Katija", "clpid": "Young-Kakani-Katija" } ], "thesis_advisor": [ { "family_name": "Dabiri", "given_name": "John O.", "orcid": "0000-0002-6722-9008", "clpid": "Dabiri-J-O" } ], "thesis_committee": [ { "family_name": "Schneider", "given_name": "Tapio", "orcid": "0000-0001-5687-2287", "clpid": "Schneider-T" }, { "family_name": "Gharib", "given_name": "Morteza", "orcid": "0000-0003-0754-4193", "clpid": "Gharib-M" }, { "family_name": "Pullin", "given_name": "Dale Ian", "clpid": "Pullin-D-I" }, { "family_name": "Dabiri", "given_name": "John O.", "orcid": "0000-0002-6722-9008", "clpid": "Dabiri-J-O" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Traditional studies of animal-fluid interactions have led to the understanding of factors that affect the distribution, ecology and energetics of swimming organisms. These interactions are commonly investigated by using quantitative flow measurement techniques, which include digital particle image velocimetry. Due to limitations in quantitative flow measurements in the natural environment, animal measurements are conducted in laboratories. Laboratory measurement techniques have been shown to have an altering impact on animal behavior and resulting flow fields. Hence, it is reasonable to question conclusions made about the impact of background flows in the natural environment from measurements conducted in the laboratory. Therefore, an apparatus that will enable the quantitative measurement of flows surrounding a swimming animal in the field is needed to accurately address the effect of background flows on animal swimming and fluid transport.
\r\n\r\nWe describe the development of a self-contained underwater velocimetry apparatus that achieves the goal of real-time, quantitative field measurements of aquatic animal-fluid interactions. Using this apparatus, we obtain measurements of flow fields surrounding animals in the field and analyze the effect of background flows on swimming animals. Using a dynamical systems technique called Lagrangian coherent structures to quantitatively compare laboratory and field-generated flows, we find that background flow structures alter fluid transport by swimming jellyfish. From these studies, we define a biologically-relevant metric for animal feeding that is based entirely on the volume of fluid that interacts with the swimming animal. The ability to quantify background flows and their influence on animal-fluid interactions will allow us to broaden our concept of animal-fluid interactions to include the effects swimming animals have on their surrounding environment. This represents a paradigm shift in the analysis of animal-fluid interactions.
\r\n\r\nRecent studies have provided heated debate about whether biologically-generated (or biogenic) mixing can have an impact in the ocean. Arguments for biogenic mixing lacked an efficient mechanism for fluid transport in viscous and stratified flow environments. We present an effective mechanism for biogenic mixing called drift, which is active during swimming, and results in permanent displacement of fluid in the direction of the animal's motion (in unstratified flow). We show that unlike mechanisms that rely on turbulent mixing generated by wake structures, drift is enhanced as viscous effects are increased. While drift has been observed in jellyfish and copepods, to understand its relevance in the global ocean, the effects of stratification need to be considered. By conducting simulations of moving bodies in stratified flow, we show that at buoyancy frequencies on the order of the mean ocean, fluid transport due to drift remains a powerful mechanism through which swimming animals may provide a significant contribution to mixing in the oceans.
", "doi": "10.7907/QJAM-9228", "publication_date": "2010", "thesis_type": "phd", "thesis_year": "2010" }, { "id": "thesis:5060", "collection": "thesis", "collection_id": "5060", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-12182008-174607", "primary_object_url": { "basename": "Thesis_2side.pdf", "content": "final", "filesize": 16076250, "license": "other", "mime_type": "application/pdf", "url": "/5060/1/Thesis_2side.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "I. Global Simulations of Interactions between Aerosols and Future Climate and II. Sensitivity of Multiangle Imaging to the Optical and Microphysical Properties of Biomass Burning Aerosols", "author": [ { "family_name": "Chen", "given_name": "Wei-Ting", "orcid": "0000-0002-9292-0933", "clpid": "Chen-Wei-Ting" } ], "thesis_advisor": [ { "family_name": "Seinfeld", "given_name": "John H.", "clpid": "Seinfeld-J-H" } ], "thesis_committee": [ { "family_name": "Wennberg", "given_name": "Paul O.", "clpid": "Wennberg-P-O" }, { "family_name": "Seinfeld", "given_name": "John H.", "clpid": "Seinfeld-J-H" }, { "family_name": "Schneider", "given_name": "Tapio", "clpid": "Schneider-T" }, { "family_name": "Yung", "given_name": "Yuk L.", "clpid": "Yung-Y-L" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "To understand the interaction between aerosols and climate, equilibrium simulations with a general circulation model are carried out in Part I to study the effects of future climate change on aerosol distributions, as well as the climate responses to future aerosol changes. The predicted warmer climate induced by carbon dioxide modifies the climate-sensitive emissions, alters the thermodynamic partitioning, and enhances wet removal of the aerosols. The direct radiative perturbations of aerosols, and the modification of clouds by aerosols can potentially change the temperature distribution, the hydrological cycle, and the atmospheric circulation; the pattern of climatic impacts from aerosols are differentiated from those of anthropogenic greenhouse gases. In Part II, the aerosol retrieval algorithm of the remote sensing instrument, the Multi-angle Imaging SpectroRadiometer (MISR), is assessed for the retrieval of biomass burning aerosols. By comparisons with coincident ground measurements and theoretical sensitivity tests, specific refinements to particle and mixture properties assumed in the algorithm for biomass burning aerosols are proposed. Representative case studies confirm the theoretical results and underline the key role of surface characterization in the remote sensing of aerosols.", "doi": "10.7907/0ZWE-9K94", "publication_date": "2009", "thesis_type": "phd", "thesis_year": "2009" }, { "id": "thesis:1962", "collection": "thesis", "collection_id": "1962", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-05222008-234331", "primary_object_url": { "basename": "Thesis_revised.pdf", "content": "final", "filesize": 34880122, "license": "other", "mime_type": "application/pdf", "url": "/1962/1/Thesis_revised.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Remote Sensing of Radiative Fluxes and Heating Rates from Satellite Instrument Measurements", "author": [ { "family_name": "Feldman", "given_name": "Daniel Robert", "orcid": "0000-0003-3365-5233", "clpid": "Feldman-Daniel-Robert" } ], "thesis_advisor": [ { "family_name": "Yung", "given_name": "Yuk L.", "clpid": "Yung-Y-L" } ], "thesis_committee": [ { "family_name": "Seinfeld", "given_name": "John H.", "clpid": "Seinfeld-J-H" }, { "family_name": "Liou", "given_name": "Kuo-Nan", "clpid": "Liou-K" }, { "family_name": "Schneider", "given_name": "Tapio", "clpid": "Schneider-T" }, { "family_name": "Yung", "given_name": "Yuk L.", "clpid": "Yung-Y-L" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Weather and climate models are required to calculate radiative fluxes and shortwave heating and longwave cooling rate profiles on a large scale. Heating and cooling rates describe the effect that different configurations of temperature, radiatively active gases, and clouds have on the rates of interlayer energy exchange and affect circulation patterns. Meanwhile, a suite of satellite-based instruments from the NASA Earth Observing System\u2019s A-Train provide an unprecedented set of measurements that can be used to produce quantities that can also yield radiative fluxes and heating and cooling rates. This work explores the extent to which passive-infrared hyperspectral measurements such as those made by the Atmospheric Infrared Sounder impart information towards infrared cooling rates. Several novel methods are explored for interpreting and retrieving cooling rates using spectral measurements.
\r\n\r\nFor scenes with optically thick clouds, however, passive visible and infrared measurements will have limited power in describing heating and cooling rates. Vertical cloud information can be obtained from several A-Train instruments: the Microwave Limb Sounder Ice Water Content product provides data on the profiles of ice clouds in the upper troposphere and this work explores how this data can be used to describe the cloud radiative effect. Recently, active-sounding measurements from CloudSat have offered an unrivalled description of cloud profiles which can be used to compute fluxes and heating rates. Preliminary CloudSat products are evaluated and a case study of heating rate analysis is presented in which CloudSat products are used to determine Tropical Tropopause Layer radiation balance.
\r\n\r\nThe radiative processes that affect the far-infrared (wavelengths of 15\u2013100 \u03bcm) are described in a limited fashion by the current suite of A-Train measurements, and yet these spectral regions have a large impact on cooling rates in the troposphere. The extra information gained by the introduction of a set of spectrally resolved far-infrared measurements is discussed for clear and cloudy scenes.
\r\n\r\nFinally, this work discusses future directions for analyzing heating rates derived from remote sensing measurements, and challenges and opportunities for future research.
\r\n", "doi": "10.7907/XMMC-F033", "publication_date": "2008", "thesis_type": "phd", "thesis_year": "2008" }, { "id": "thesis:4990", "collection": "thesis", "collection_id": "4990", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-12132007-145150", "primary_object_url": { "basename": "Thesis_ZMY.pdf", "content": "final", "filesize": 4034099, "license": "other", "mime_type": "application/pdf", "url": "/4990/1/Thesis_ZMY.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Constraining Global Carbon Budget Using Vertically-Integrated CO\u2082 Measurements", "author": [ { "family_name": "Yang", "given_name": "Zhonghua", "clpid": "Yang-Zhonghua" } ], "thesis_advisor": [ { "family_name": "Wennberg", "given_name": "Paul O.", "clpid": "Wennberg-P-O" } ], "thesis_committee": [ { "family_name": "Adkins", "given_name": "Jess F.", "clpid": "Adkins-J-F" }, { "family_name": "Wennberg", "given_name": "Paul O.", "clpid": "Wennberg-P-O" }, { "family_name": "Toon", "given_name": "Geoffrey C.", "clpid": "Toon-G-C" }, { "family_name": "Randerson", "given_name": "James T.", "clpid": "Randerson-J-T" }, { "family_name": "Schneider", "given_name": "Tapio", "clpid": "Schneider-T" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "I demonstrate that high precision measurements of the vertical-average dry volumn-mixing-ratio of atmospheric carbon dioxide (CO2 ) can be obtained from ground-based solar spectra. Oxygen measurements from the same spectra can be used to calibrate CO2 retrievals across different instruments, enabling a global network of column CO2 observations to be constructed. I also illustrate that this new type of data, together with aircraft pro\ufb01le CO2 observations, provide new constraints on global carbon \ufb02uxes.\r\n", "doi": "10.7907/3XR2-7185", "publication_date": "2008", "thesis_type": "phd", "thesis_year": "2008" }, { "id": "thesis:14", "collection": "thesis", "collection_id": "14", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-01032007-154646", "primary_object_url": { "basename": "Jiang-thesis-allchapter-Aug28-2006.pdf", "content": "final", "filesize": 9672783, "license": "other", "mime_type": "application/pdf", "url": "/14/1/Jiang-thesis-allchapter-Aug28-2006.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "I: Interannual Variability of Stratospheric Ozone and Temperature. II: Seasonal Cycle of N\u2082O", "author": [ { "family_name": "Jiang", "given_name": "Xun", "orcid": "0000-0001-8932-3807", "clpid": "Jiang-Xun" } ], "thesis_advisor": [ { "family_name": "Yung", "given_name": "Yuk L.", "clpid": "Yung-Y-L" } ], "thesis_committee": [ { "family_name": "Ingersoll", "given_name": "Andrew P.", "clpid": "Ingersoll-A-P" }, { "family_name": "Wennberg", "given_name": "Paul O.", "clpid": "Wennberg-P-O" }, { "family_name": "Schneider", "given_name": "Tapio", "clpid": "Schneider-T" }, { "family_name": "Yung", "given_name": "Yuk L.", "clpid": "Yung-Y-L" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "This dissertation is a collection of empirical and modeling studies focusing on the interannual variability (IAV) of the stratospheric ozone and temperature. The IAV of O\u2083 in the high latitude is characterized by four main modes in both hemispheres. Similar spatial patterns and trends are simulated by the Goddard Earth Observation System, Version 4 (GEOS-4) chemistry-climate model (CCM). The El Ni\u00f1o-Southern Oscillation signal in column ozone is also simulated well by the GEOS-4 CCM in the tropics.
\r\n\r\nTo study the Quasi-biennial oscillation (QBO) and QBO-Annual Beat (QBO-AB) in column ozone, the Caltech/JPL two-dimensional (2-D) chemistry and transport model (CTM) has been used. The 2-D CTM provides realistic simulations of the seasonal and IAV of ozone in the tropics. The phase and amplitude of the QBO are well captured by the model. The QBO-AB found in the simulated ozone agrees well with that in the observed data. An idealized 2-D interactive chemistry, radiation, and dynamic model (CRDM) is used to investigate the spatial patterns of, and mechanism for, the QBO-AB signal in ozone in the tropics and subtropics. An extended EOF analysis reveals the characteristic pattern of the downward propagation of QBO and upward propagation of QBO-AB. The model results are compared to those from the Merged Ozone Data.
\r\n\r\nTo understand the IAV and trend in the stratospheric temperature, we apply principal component analysis to observations and global climate model simulations. The cooling trend in the stratosphere is associated with a spatially uniform pattern of stratospheric variability, which is isolated from more common modes of natural IAV such as the Northern Annular Mode. These results are supported by a number of coupled ocean-atmosphere climate model simulations.
\r\n\r\nFinally, a systematic study of the seasonal cycle and its latitudinal variation is carried out for the nitrous oxide data. In order to confirm the weak seasonal signal in the observations, we applied the multi-taper method for the spectrum analysis. The amplitude (peak to peak) of the seasonal cycle of N\u2082O varies from 0.29 ppb (parts-per-billion by mole fraction in dry air) at the South Pole to 1.15 ppb at Alert.
", "doi": "10.7907/4022-0X13", "publication_date": "2007", "thesis_type": "phd", "thesis_year": "2007" }, { "id": "thesis:2339", "collection": "thesis", "collection_id": "2339", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-05312007-133239", "primary_object_url": { "basename": "henze_thesis_final.pdf", "content": "final", "filesize": 15015624, "license": "other", "mime_type": "application/pdf", "url": "/2339/1/henze_thesis_final.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Forward and Inverse Analysis of Chemical Transport Models", "author": [ { "family_name": "Henze", "given_name": "Daven Ker", "orcid": "0000-0001-6431-4963", "clpid": "Henze-Daven-Ker" } ], "thesis_advisor": [ { "family_name": "Seinfeld", "given_name": "John H.", "clpid": "Seinfeld-J-H" } ], "thesis_committee": [ { "family_name": "Seinfeld", "given_name": "John H.", "clpid": "Seinfeld-J-H" }, { "family_name": "Li", "given_name": "Qinbin", "clpid": "Li-Q" }, { "family_name": "Flagan", "given_name": "Richard C.", "clpid": "Flagan-R-C" }, { "family_name": "Schneider", "given_name": "Tapio", "clpid": "Schneider-T" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Assessing the discrepancy between modeled and observed distributions of aerosols is a persistent problem on many scales. Tools for analyzing the evolution of aerosol size distributions using the adjoint method are presented in idealized box model calculations. The ability to recover information about aerosol growth rates and initial size distributions is assessed given a range of simulated observations of evolving systems. While such tools alone could facilitate analysis of chamber measurements, improving estimates of aerosol sources on regional and global scales requires explicit consideration of many additional chemical and physical processes that govern secondary formation of atmospheric aerosols from emissions of gas-phase precursors. The adjoint of the global chemical transport model GEOS-Chem is derived, affording detailed analysis of the relationship between gas-phase aerosol precursor emissions (SOx, NOx, and NH3) and the subsequent distributions of sulfate - ammonium - nitrate aerosol. Assimilation of surface measurements of sulfate and nitrate aerosol is shown to provide valuable constraints on emissions of ammonia. Adjoint sensitivities are used to propose strategies for air quality control, suggesting, for example, that reduction of SOx emissions in the summer and NH3 emissions in the winter would most effectively reduce non-attainment of aerosol air quality standards. The ability of this model to estimate global distributions of carbonaceous aerosol is also addressed. Based on new yield data from environmental chamber studies, mechanisms for incorporating the dependence of secondary organic aerosol (SOA) formation on NOx concentrations are developed for use in global models. When NOx levels are appropriately accounted for, it is demonstrated that sources such as isoprene and aromatics, previously neglected as sources of aerosol in global models, significantly contribute to predicted SOA burdens downwind of polluted areas (owing to benzene and toluene) and in the free troposphere (owing to isoprene).", "doi": "10.7907/5647-T777", "publication_date": "2007", "thesis_type": "phd", "thesis_year": "2007" }, { "id": "thesis:2105", "collection": "thesis", "collection_id": "2105", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-05262006-111949", "primary_object_url": { "basename": "thesis_nyk.pdf", "content": "final", "filesize": 1927391, "license": "other", "mime_type": "application/pdf", "url": "/2105/1/thesis_nyk.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Characterizing Carbon-Dioxide Fluxes from Oceans and Terrestrial Ecosystems", "author": [ { "family_name": "Krakauer", "given_name": "Nir Yitzhak", "orcid": "0000-0002-4926-5427", "clpid": "Krakauer-Nir-Yitzhak" } ], "thesis_advisor": [ { "family_name": "Schneider", "given_name": "Tapio", "clpid": "Schneider-T" } ], "thesis_committee": [ { "family_name": "Schneider", "given_name": "Tapio", "clpid": "Schneider-T" }, { "family_name": "Adkins", "given_name": "Jess F.", "clpid": "Adkins-J-F" }, { "family_name": "Randerson", "given_name": "James T.", "clpid": "Randerson-J-T" }, { "family_name": "Wennberg", "given_name": "Paul O.", "clpid": "Wennberg-P-O" }, { "family_name": "Yung", "given_name": "Yuk L.", "clpid": "Yung-Y-L" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "Understanding the processes that change the amount of carbon stored in the ocean and in the land biota, with their implications for future climate and ecology, is a fundamental goal of earth-system science. I have developed, refined, and applied several approaches that combine data analysis and modeling to better understand processes affecting carbon fluxes.
\r\n\r\n(1) Using a database of tree-ring widths from some 40,000 trees, I looked at the impact of large volcanic eruptions in the past millennium on tree growth globally. I found a decline in growth north of 45\u00b0 N lasting for several years after eruptions, presumably due to eruption-associated cooling, and no significant impact at lower latitudes. This argues against the hypothesis that the increased diffuse-light fraction due to volcanic aerosols greatly increased plant carbon uptake after the 1991 Pinatubo eruption, suggesting that other explanations are needed for the slow increase in atmospheric CO2 levels in the early 1990s.
\r\n\r\n(2) I applied generalized cross-validation (GCV) to the problem of estimating a regional CO2 source/sink pattern consistent with observed geographic variation in atmosphere CO2 levels. I showed that GCV works for selecting data and regional-flux uncertainty levels to assume for this inverse problem; these have usually been estimated rather arbitrarily, though they can have a large impact on the solution.
\r\n\r\n(3) The air-sea gas transfer velocity determines how fast the surface ocean adjusts to a change in atmospheric composition, and hence is important for understanding ocean CO2 uptake. By modeling the ocean\u2019s adjustment to fluctuations in atmospheric carbon isotope composition and analyzing a variety of atmosphere and ocean bomb-14C and 13C measurements, I estimated regional and global mean gas transfer velocities, concluding that there may be less latitudinal variation in the gas transfer velocity than usually thought \u2013 implying, for example, relatively low CO2 uptake in the Southern Ocean.
", "doi": "10.7907/8B12-1G19", "publication_date": "2006", "thesis_type": "phd", "thesis_year": "2006" }, { "id": "thesis:2065", "collection": "thesis", "collection_id": "2065", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-05252006-223939", "primary_object_url": { "basename": "thesis_liu.pdf", "content": "final", "filesize": 1682415, "license": "other", "mime_type": "application/pdf", "url": "/2065/1/thesis_liu.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Interaction of Magnetic Field and Flow in the Outer Shells of Giant Planets", "author": [ { "family_name": "Liu", "given_name": "Junjun", "clpid": "Liu-Junjun" } ], "thesis_advisor": [ { "family_name": "Stevenson", "given_name": "David John", "clpid": "Stevenson-D-J" }, { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" }, { "family_name": "Ingersoll", "given_name": "Andrew P.", "clpid": "Ingersoll-A-P" } ], "thesis_committee": [ { "family_name": "Ingersoll", "given_name": "Andrew P.", "orcid": "0000-0002-2035-9198", "clpid": "Ingersoll-A-P" }, { "family_name": "Stevenson", "given_name": "David John", "orcid": "0000-0001-9432-7159", "clpid": "Stevenson-D-J" }, { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" }, { "family_name": "Sari", "given_name": "Re'em", "orcid": "0000-0002-1084-3656", "clpid": "Sari-R" }, { "family_name": "Schneider", "given_name": "Tapio", "orcid": "0000-0001-5687-2287", "clpid": "Schneider-T" } ], "local_group": [ { "literal": "TAPIR" }, { "literal": "Astronomy Department" }, { "literal": "div_gps" } ], "abstract": "This study of the interaction of magnetic field and flow in the outer shells of giant planets consists of three parts.
\r\n\r\nPart one: The atmospheres of Jupiter and Saturn exhibit strong and stable zonal winds. Busse suggested that they might be the surface expression of deep flows on cylinders. However, the deep flow hypothesis experiences difficulty when account is taken of the electrical conductivity of molecular hydrogen as measured in shockwave experiments. The deep zonal flow of an electrically conducting fluid would produce a toroidal magnetic field, an associated poloidal electrical current, and Ohmic dissipation. In steady state, the total Ohmic dissipation cannot exceed the planet's net luminosity. If we assume that the observed zonal flow penetrates along cylinders until it is truncated to (near) zero at some spherical radius, the upper bound on Ohmic dissipation constrains this radius to be no smaller than 0.95 Jupiter radius and 0.87 Saturn radius. The truncation of the cylindrical flow in the convective envelope requires an appropriate force to break the Taylor-Proudman constraint. We have been unable to identify any plausible candidate. Thus we conclude that deep-seated cylindrical flows do not exist.
\r\n\r\nPart two: A fluid shell with sufficient electrical conductivity and azimuthal velocity shear outside of the dynamo generation region can attenuate the non-axisymmetric component of the magnetic field. However, the interaction of the axisymmetric component of the magnetic field and the zonal flow is able to reduce the magnitude of zonal flow. The dimensionless number characterizing this reduction is the Chandrasekhar number. The smaller Saturnian field may allow a larger velocity shear and a greater attenuation of the non-axisymmetric field, thereby providing a possible explanation for the nearly axisymmetric field.
\r\n\r\nPart three: Combining the study for the attenuation effect produced by the semi-conducting layer and the observation of the magnetic field by Galileo and Voyager, we find the possible outer boundary of the dynamo generation zone is at 0.86 Jupiter radius. The magnetic fields generated in the outer shell are dictated by a length scale comparable to the scale height of electrical conductivity, which is much smaller than the radius of the planet.
", "doi": "10.7907/4PVM-0G30", "publication_date": "2006", "thesis_type": "phd", "thesis_year": "2006" }, { "id": "thesis:2156", "collection": "thesis", "collection_id": "2156", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-05272005-145538", "primary_object_url": { "basename": "vwmain.pdf", "content": "final", "filesize": 3942640, "license": "other", "mime_type": "application/pdf", "url": "/2156/1/vwmain.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "On the Richtmyer-Meshkov Instability in Magnetohydrodynamics", "author": [ { "family_name": "Wheatley", "given_name": "Vincent", "orcid": "0000-0002-7287-7659", "clpid": "Wheatley-Vincent" } ], "thesis_advisor": [ { "family_name": "Pullin", "given_name": "Dale Ian", "clpid": "Pullin-D-I" } ], "thesis_committee": [ { "family_name": "Pullin", "given_name": "Dale Ian", "clpid": "Pullin-D-I" }, { "family_name": "Leonard", "given_name": "Anthony", "clpid": "Leonard-A" }, { "family_name": "Shepherd", "given_name": "Joseph E.", "orcid": "0000-0003-3181-9310", "clpid": "Shepherd-J-E" }, { "family_name": "Schneider", "given_name": "Tapio", "orcid": "0000-0001-5687-2287", "clpid": "Schneider-T" }, { "family_name": "Colonius", "given_name": "Tim", "orcid": "0000-0003-0326-3909", "clpid": "Colonius-T" } ], "local_group": [ { "literal": "GALCIT" }, { "literal": "div_eng" } ], "abstract": "The Richtmyer-Meshkov instability is important in a wide variety of applications including inertial confinement fusion and astrophysical phenomena. In some of these applications, the fluids involved may be plasmas and hence be affected by magnetic fields. For one configuration, it has been numerically demonstrated that the growth of the instability in magnetohydrodynamics is suppressed in the presence of a magnetic field. Here, the nature of this suppression is theoretically and numerically investigated.
\r\n\r\nIn the framework of ideal incompressible magnetohydrodynamics, we examine the stability of an impulsively accelerated, sinusoidally perturbed density interface in the presence of a magnetic field that is parallel to the acceleration. This is accomplished by analytically solving the linearized initial value problem, which is a model for the Richtmyer-Meshkov instability. We find that the initial growth rate of the interface is unaffected by the presence of a magnetic field, but for a finite magnetic field the interface amplitude asymptotes to a constant value. Thus the instability of the interface is suppressed. The interface behavior from the analytical solution is compared to the results of both linearized and non-linear compressible numerical simulations for a wide variety of conditions.
\r\n\r\nWe then consider the problem of the regular refraction of a shock at an oblique, planar contact discontinuity separating conducting fluids of different densities in the presence of a magnetic field aligned with the incident shock velocity. Planar ideal MHD simulations indicate that the presence of a magnetic field inhibits the deposition of vorticity on the shocked contact, which leads to the suppression of the Richtmyer-Meshkov instability. We show that the shock refraction process produces a system of five to seven plane waves that may include fast, intermediate, and slow MHD shocks, slow compound waves, 180\u00b0 rotational discontinuities, and slow-mode expansion fans that intersect at a point. In all solutions, the shocked contact is vorticity free and hence stable. These solutions are not unique, but differ in the type of waves that participate. The set of equations governing the structure of these multiple-wave solutions is obtained in which fluid property variation is allowed only in the azimuthal direction about the wave-intersection point. Corresponding solutions are referred to as either quintuple-points, sextuple-points, or septuple-points, depending on the number of participating waves. A numerical method of solution is described and examples are compared to the results of numerical simulations for moderate magnetic field strengths. The limit of vanishing magnetic field at fixed permeability and pressure is studied for two solution types. The relevant solutions correspond to the hydrodynamic triple-point with the shocked contact replaced by a singular structure consisting of a wedge, whose angle scales with the applied field magnitude, bounded by either two slow compound waves or two 180\u00b0 rotational discontinuities, each followed by a slow-mode expansion fan. These bracket the MHD contact which itself cannot support a tangential velocity jump in the presence of a non-parallel magnetic field. The magnetic field within the singular wedge is finite and the shock-induced change in tangential velocity across the wedge is supported by the expansion fans that form part of the compound waves or follow the rotational discontinuities. To verify these findings, an approximate leading order asymptotic solution appropriate for both flow structures was computed. The full and asymptotic solutions are compared quantitatively and there is shown to be excellent agreement between the two.
", "doi": "10.7907/N407-2B54", "publication_date": "2005", "thesis_type": "phd", "thesis_year": "2005" }, { "id": "thesis:2089", "collection": "thesis", "collection_id": "2089", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-05262005-100534", "primary_object_url": { "basename": "BhatThesis_05_26_2005.pdf", "content": "final", "filesize": 1917954, "license": "other", "mime_type": "application/pdf", "url": "/2089/1/BhatThesis_05_26_2005.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Lagrangian Averaging, Nonlinear Waves, and Shock Regularization", "author": [ { "family_name": "Bhat", "given_name": "Harish Subrahmanya", "orcid": "0000-0001-7631-1831", "clpid": "Bhat-Harish-Subrahmanya" } ], "thesis_advisor": [ { "family_name": "Marsden", "given_name": "Jerrold E.", "clpid": "Marsden-J-E" } ], "thesis_committee": [ { "family_name": "Marsden", "given_name": "Jerrold E.", "clpid": "Marsden-J-E" }, { "family_name": "Hajimiri", "given_name": "Ali", "clpid": "Hajimiri-A" }, { "family_name": "Fetecau", "given_name": "Razvan Constantin", "clpid": "Fetecau-R-C" }, { "family_name": "Murray", "given_name": "Richard M.", "clpid": "Murray-R-M" }, { "family_name": "Schneider", "given_name": "Tapio", "clpid": "Schneider-T" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "In this thesis, we explore various models for the flow of a compressible fluid as well as model equations for shock formation, one of the main features of compressible fluid flows.
\r\n\r\nWe begin by reviewing the variational structure of compressible fluid mechanics. We derive the barotropic compressible Euler equations from a variational principle in both material and spatial frames. Writing the resulting equations of motion requires certain Lie-algebraic calculations that we carry out in detail for expository purposes.
\r\n\r\nNext, we extend the derivation of the Lagrangian averaged Euler (LAE-alpha) equations to the case of barotropic compressible flows. The derivation in this thesis involves averaging over a tube of trajectories centered around a given Lagrangian flow. With this tube framework, the LAE-alpha equations are derived by following a simple procedure: start with a given action, expand via Taylor series in terms of small-scale fluid fluctuations, truncate, average, and then model those terms that are nonlinear functions of the fluctuations.
\r\n\r\nWe then analyze a one-dimensional subcase of the general models derived above. We prove the existence of a large family of traveling wave solutions. Computing the dispersion relation for this model, we find it is nonlinear, implying that the equation is dispersive. We carry out numerical experiments that show that the model possesses smooth, bounded solutions that display interesting pattern formation.
\r\n\r\nFinally, we examine a Hamiltonian partial differential equation (PDE) that regularizes the inviscid Burgers equation without the addition of standard viscosity. Here alpha is a small parameter that controls a nonlinear smoothing term that we have added to the inviscid Burgers equation. We show the existence of a large family of traveling front solutions. We analyze the initial-value problem and prove well-posedness for a certain class of initial data. We prove that in the zero-alpha limit, without any standard viscosity, solutions of the PDE converge strongly to weak solutions of the inviscid Burgers equation. We provide numerical evidence that this limit satisfies an entropy inequality for the inviscid Burgers equation. We demonstrate a Hamiltonian structure for the PDE.
", "doi": "10.7907/8DJ2-F672", "publication_date": "2005", "thesis_type": "phd", "thesis_year": "2005" }, { "id": "thesis:2162", "collection": "thesis", "collection_id": "2162", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-05272005-163801", "primary_object_url": { "basename": "Faddy_PhD.pdf", "content": "final", "filesize": 14558318, "license": "other", "mime_type": "application/pdf", "url": "/2162/1/Faddy_PhD.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Flow Structure in a Model of Aircraft Trailing Vortices", "author": [ { "family_name": "Faddy", "given_name": "James Malcolm", "clpid": "Faddy-James-Malcolm" } ], "thesis_advisor": [ { "family_name": "Pullin", "given_name": "Dale Ian", "clpid": "Pullin-D-I" } ], "thesis_committee": [ { "family_name": "Pullin", "given_name": "Dale Ian", "clpid": "Pullin-D-I" }, { "family_name": "Leonard", "given_name": "Anthony", "clpid": "Leonard-A" }, { "family_name": "Hornung", "given_name": "Hans G.", "orcid": "0000-0002-4903-8419", "clpid": "Hornung-H-G" }, { "family_name": "Schneider", "given_name": "Tapio", "orcid": "0000-0001-5687-2287", "clpid": "Schneider-T" }, { "family_name": "Colonius", "given_name": "Tim", "orcid": "0000-0003-0326-3909", "clpid": "Colonius-T" } ], "local_group": [ { "literal": "GALCIT" }, { "literal": "div_eng" } ], "abstract": "We consider a model of incompressible trailing vortices consisting of an array of counter-rotating structures in a doubly periodic domain, infinite in the vertical direction. The two-dimensional vortex array of Mallier and Maslowe is combined with an axial velocity profile chosen proportional to the initial axial vorticity to provide an initial condition for the vortex wake. This base flow is a weak solution of the three component steady Euler equations in two dimensions thus allowing its linear stability properties to be investigated. These are used to interpret several stages in the development of vortex structure observed in fully three-dimensional DNS at Reynolds numbers Gamma/(2 pi nu)=O(1000). For sufficiently high axial velocity, itseffect can be seen, in that each vortex in the linear array first develops helical structures before undergoing a period of relaminarization. At later times the more slowly growing co-operative elliptical instabilities become apparent; however, the helical structure persists and the observed vortical structures remain coherent for longer periods than in the absence of axial velocity. Using the stretched vortex subgrid model, large-eddy simulation runs are performed at higher Reynolds numbers and a mixing transition identified at about Re = 1-2 x 10\u2074. Similar phenomena are observed in these simulations as are seen in the DNS. Next the spatial nature of the true aircraft wake is compared to the temporal approximation commonly employed to simplify the computational complexity of the problem. A model is formulated to acount for the average axial pressure gradients that develops in the spatial wake but is absent from the temporal simulation. The model enables jet- and wake-like axial flows to be distinguished and the subtle differences in the ensuing turbulent states investigated. Finally, the model is used to investigate co-rotating vortex merger, the new thrust term providing a mechanism to enhance the axial flow further destabilizing the base flow.", "doi": "10.7907/RC42-JY40", "publication_date": "2005", "thesis_type": "phd", "thesis_year": "2005" }, { "id": "thesis:427", "collection": "thesis", "collection_id": "427", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-02012005-131605", "primary_object_url": { "basename": "ChungThesis2.pdf", "content": "final", "filesize": 3579858, "license": "other", "mime_type": "application/pdf", "url": "/427/1/ChungThesis2.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Global Distribution, Radiative Forcing, and Climate Impact of Carbonaceous Aerosols", "author": [ { "family_name": "Chung", "given_name": "Serena Hsin-Yi", "orcid": "0000-0001-5030-5871", "clpid": "Chung-Serena-Hsin-Yi" } ], "thesis_advisor": [ { "family_name": "Seinfeld", "given_name": "John H.", "clpid": "Seinfeld-J-H" } ], "thesis_committee": [ { "family_name": "Seinfeld", "given_name": "John H.", "clpid": "Seinfeld-J-H" }, { "family_name": "Wennberg", "given_name": "Paul O.", "clpid": "Wennberg-P-O" }, { "family_name": "Flagan", "given_name": "Richard C.", "clpid": "Flagan-R-C" }, { "family_name": "Schneider", "given_name": "Tapio", "clpid": "Schneider-T" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "This thesis is motivated by the need to better understand and quantify the climate effects of carbonaceous aerosols, i.e., black carbon (BC) and organic carbon (OC). Global three-dimensional distribution of carbonaceous aerosols is simulated online in a general circulation model (GCM). The carbonaceous aerosol model includes primary BC, primary OC, five groups of biogenic volatile organic compounds (BVOCs), and fourteen semi-volatile products of BVOC oxidation by O3, OH, and NO3, which condense to form secondary organic aerosols (SOAs) based on an equilibrium partitioning model. Human activities since the preindustrial period are predicted to have increased global burdens of BC and OC by an order of magnitude and almost tripled the SOA production rate. Based on an older emission inventory for BC, the direct radiative forcing of increased atmospheric BC burden is estimated to warm the atmosphere by 0.51 to 0.8 W m-2, depending on how BC is mixed with other tropospheric aerosols. For OC, the estimated anthropogenic direct radiative forcing at top of the atmosphere (TOA) is -0.1 to -0.2 W m-2, depending on the water-uptake property of OC. When BC, OC and sulfate are combined, the estimated direct radiative forcing at TOA is -0.39 to -0.78 W m-2. Using an updated emission inventory, direct radiative forcing of anthropogenic BC at TOA is estimated to be +0.33 and +0.6 W m-2, for BC mixed externally and internally with present-day level of sulfate, respectively. Using a GCM coupled to a mixed-layer ocean model, these estimated forcings for BC are predicted to warm surface air temperature by 0.2 to 0.37 K. The temperature increase is the largest over northern high latitutdes during winter and early spring. Even though the predicted global-averaged warming due to BC is less than that of greenhouse gases, significant regional differences do exist, such as substantial warming in central and eastern Russia predicted for BC. In addition to temperature increase, direct radiative forcing of anthropogenic BC is also predicted to lead to a change in the hydrological cycle by shifting the intertropical convergence zone northward.", "doi": "10.7907/d2ff-ad43", "publication_date": "2005", "thesis_type": "phd", "thesis_year": "2005" }, { "id": "thesis:2492", "collection": "thesis", "collection_id": "2492", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-06072004-161416", "primary_object_url": { "basename": "west_thesis.pdf", "content": "final", "filesize": 3182832, "license": "other", "mime_type": "application/pdf", "url": "/2492/1/west_thesis.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Variational Integrators", "author": [ { "family_name": "West", "given_name": "Matthew", "orcid": "0000-0002-7605-0050", "clpid": "West-Matthew" } ], "thesis_advisor": [ { "family_name": "Marsden", "given_name": "Jerrold E.", "clpid": "Marsden-J-E" } ], "thesis_committee": [ { "family_name": "Marsden", "given_name": "Jerrold E.", "clpid": "Marsden-J-E" }, { "family_name": "Beck", "given_name": "James L.", "clpid": "Beck-J-L" }, { "family_name": "Burdick", "given_name": "Joel Wakeman", "orcid": "0000-0002-3091-540X", "clpid": "Burdick-J-W" }, { "family_name": "Schroeder", "given_name": "Peter", "orcid": "0000-0002-0323-7674", "clpid": "Schr\u00f6der-P" }, { "family_name": "Schneider", "given_name": "Tapio", "orcid": "0000-0001-5687-2287", "clpid": "Schneider-T" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Variational integrators are a class of discretizations for mechanical systems which are derived by discretizing Hamilton's principle of stationary action. They are applicable to both ordinary and partial differential equations, and to both conservative and forced problems. In the absence of forcing they conserve (multi-)symplectic structures, momenta arising from symmetries, and energy up to a bounded error.
\r\n\r\nIn this thesis the basic theory of discrete variational mechanics for ordinary differential equations is developed in depth, and is used as the basis for constructing variational integrators and analyzing their numerical properties. This is then taken as the starting point for the development of a new class of asynchronous time stepping methods for solid mechanics, known as Asynchronous Variational Integrators (AVIs). These explicit methods time step different elements in a finite element mesh with fully independent and decoupled time steps, allowing the simulation to proceed locally at the fastest rate allowed by local stability restrictions. Numerical examples of AVIs are provided, demonstrating the excellent properties they posess by virtue of their variational derivation.
", "doi": "10.7907/CMZ1-RQ16", "publication_date": "2004", "thesis_type": "phd", "thesis_year": "2004" }, { "id": "thesis:2437", "collection": "thesis", "collection_id": "2437", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-06042004-131001", "primary_object_url": { "basename": "dissertation.pdf", "content": "final", "filesize": 4935571, "license": "other", "mime_type": "application/pdf", "url": "/2437/1/dissertation.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Temporal and Spatial Patterns of the Interannual Variability of Stratospheric Ozone and Dynamics", "author": [ { "family_name": "Camp", "given_name": "Charles David", "orcid": "0000-0003-0295-7861", "clpid": "Camp-Charles-David" } ], "thesis_advisor": [ { "family_name": "Yung", "given_name": "Yuk L.", "clpid": "Yung-Y-L" } ], "thesis_committee": [ { "family_name": "Candes", "given_name": "Emmanuel J.", "clpid": "Candes-E-J" }, { "family_name": "Bruno", "given_name": "Oscar P.", "clpid": "Bruno-O-P" }, { "family_name": "Schneider", "given_name": "Tapio", "clpid": "Schneider-T" }, { "family_name": "Yung", "given_name": "Yuk L.", "clpid": "Yung-Y-L" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "This dissertation is a collection of empirical and modeling studies focusing on the interannual variability (IAV) of stratospheric ozone and the dynamics associated with that variability. Empirical analyses of the IAV of total column ozone in the tropics and midlatitudes are performed using the Merged Ozone Data (MOD) set. MOD combines the monthly mean column abundances collected by the Total Ozone Mapping Spectrometer and the Solar Backscatter Ultraviolet instruments, provides a nearly continuous record from late 1978 to present on a 2D grid. The first four EOFs from principal component analyses of MOD capture over 93% (82%) of the variance of the tropical (midlatitude) IAV. These analyses display structures attributable to the quasi-biennial oscillation (QBO), with influence from a decadal oscillation, an interaction between the QBO and an annual cycle (QBO-AB), and ENSO. Similar decompositions occur for dynamical fields from the NCEP/NCAR reanalysis. Using these analyses, we found possible connections between the deduced patterns in ozone and the climate variables. For comparison to the observations, a 2D chemistry and transport model (CTM) was used to simulate the ozone IAV. The NCEP/Department of Energy (DOE) Reanalysis 2 data are used to derive a monthly mean meridional circulation from 1979 to 2002 which is then used to drive the Caltech/JPL 2D CTM, allowing for an investigation of the impact of dynamics on the interannual variability (IAV) of the total column ozone for all years for which the MOD is available. The 2D CTM provides realistic simulations of the seasonal and IAV of ozone in the tropics, reasonable agreement in the NH midlatitudes but poor agreement in the SH midlatitudes. The influence of the QBO and QBO-AB are well represented in the simulation. A 71-year record of column ozone from Arosa, Switzerland is analyzed using singular spectrum analysis (SSA). The SSA decomposition separates the signals from the seasonal cycle, QBO, QBO-AB, and decadal oscillations. A 3.5-year oscillation is also discovered. A nonlinear trend is extracted and nonstationary behavior of some of the oscillations is found. Finally, a connection between fluctuations in stratospheric ozone and in tropospheric methane is observed and modeled.", "doi": "10.7907/A4EC-6M08", "publication_date": "2004", "thesis_type": "phd", "thesis_year": "2004" }, { "id": "thesis:1590", "collection": "thesis", "collection_id": "1590", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-05032004-150434", "primary_object_url": { "basename": "alltogether_final_version.pdf", "content": "final", "filesize": 7475919, "license": "other", "mime_type": "application/pdf", "url": "/1590/1/alltogether_final_version.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "I. Variability of the Outgoing Thermal IR Spectra and Its Application in GCM Validation. II. The Detection of Cloud/Aerosol in the Outgoing Thermal IR Spectra", "author": [ { "family_name": "Huang", "given_name": "Xianglei", "orcid": "0000-0002-7129-614X", "clpid": "Huang-Xianglei" } ], "thesis_advisor": [ { "family_name": "Yung", "given_name": "Yuk L.", "clpid": "Yung-Y-L" } ], "thesis_committee": [ { "family_name": "Wennberg", "given_name": "Paul O.", "clpid": "Wennberg-P-O" }, { "family_name": "Ingersoll", "given_name": "Andrew P.", "clpid": "Ingersoll-A-P" }, { "family_name": "Richardson", "given_name": "Mark I.", "clpid": "Richardson-M-I" }, { "family_name": "Schneider", "given_name": "Tapio", "clpid": "Schneider-T" }, { "family_name": "Yung", "given_name": "Yuk L.", "clpid": "Yung-Y-L" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "The theme of this thesis is studying the outgoing thermal IR spectra of Earth and Mars. It is divided into two parts: the first part (Chapters 1-4) is focused on the variability seen in the outgoing thermal IR spectra and its application in validating model simulation, and the second part (Chapters 5-6) concentrates on the detection of cirrus (cirrus/dust aerosol) from terrestrial (Martian) outgoing thermal IR spectra.
\r\n\r\nIn Chapter 1, an example of climate change seen from two spectrometers seperated by 26 years is used to illustrate the singular importance of the outgoing thermal IR spectra in climate observations. The importance of testing the variability of models and the feasibility of using the outgoing thermal IR spectra in such tests are discussed.
\r\n\r\nIn Chapter 2, a study of the temporal variability at the tropical and midlatitude Pacific Oceans seen from IRIS (Infrared Interferometer Spectrometer) spectra and corresponding synthetic spectra based on simulations from two GCMs (UCLA GCM and NCAR CAM2) is presented. The discrepancies between modeled and observed temporal variability are substantial. The differences between two GCMs are also significant. Further examination shows that these discrepancies are insensitive to the parameterization of cloud optical properties and most likely due to deficiencies in simulating the seasonal and intraseasonal variations of the Walker Circulation in the tropical Pacific and the seasonal variations of boundary-layer temperature, low cloud, and stratospheric temperature in the midlatitude Pacific.
\r\n\r\nIn Chapter 3, a survey of the spatial variability seen from AIRS (Atmospheric Infrared Sounder) spectra and corresponding synthetic spectra based on NCAR CAM2 simulation is presented. To a large extent, the simulated spatial variability agrees well with the observed counterpart. The major discrepancies between model and observation can be attributed to the incorrect location of ITCZ in the western Pacific, the underrepresented dust aerosol at the Arabian Sea and off the Atlantic Coast of North Africa, and the overestimated spatial variation of stratospheric temperature in the model.
\r\n\r\nChapter 4 presents a comparative study of the temporal and spatial variability seen in the Martian outgoing thermal IR spectra collected by MGS-TES (Thermal Emission Spectrometer). Surface temperature variation is the dominant contributor to the temporal and spatial variability seen here. The variations of CO2 column abundance, dust aerosol and water ice cloud associated with topography, as well as the imprint of dust storms, can be also seen from such analysis. The negative correlation between dust and water ice spectral features seen from this analysis suggests that, to some extent, dust and water ice cloud are mutually exclusive of each other in the Martian atmosphere.
\r\n\r\nChapter 5 presents a sensitivity study of identifying optically thin cirrus from high-resolution (each individual absorption line is almost resolved) thermal IR spectra based on the line shapes of the residual spectra. This cirrus-detection approach is different from all previous cirrus-detection algorithms in the sense of making use of information content contained in the high-resolution measurements.
\r\n\r\nChapter 6 presents a tri-spectral algorithm to detect water ice cloud, dust, and surface anisothermality from low-resolution Martian outgoing thermal IR spectra, such as MGS-TES spectra. This algorithm is complementary to any more sophisticated retrieval scheme and can be used to screen large amounts of data to get a quick overview.
", "doi": "10.7907/0J28-W457", "publication_date": "2004", "thesis_type": "phd", "thesis_year": "2004" } ]