Implementation of the Global Positioning System (GPS) network of satellites and\r\nsmall, high performance instrumentation to receive GPS signals have created an\r\nopportunity for low cost, active remote sounding of Earth's atmosphere by radio\r\noccultation. The first goal of the present research is to estimate the spatial coverage,\r\nresolution and accuracy expected for atmospheric profiles derived from GPS occultations.\r\nTypically, vertical resolution ranges from 0.5 km in the lower troposphere to 1.4 km in the\r\nmiddle atmosphere. Useful profiles of refractivity should be derivable from ~60 km\r\naltitude to the surface with the exception of regions less than 250 m in vertical extent\r\nassociated with high vertical humidity gradients. Above the 250 K altitude level in the\r\ntroposphere, where the effects of water are negligible, sub-Kelvin temperature accuracy is\r\npredicted up to ~40 km depending on the phase of the solar cycle. Predicted accuracy of\r\ngeopotential heights of constant pressure levels is ~10 m or better between 10 and 20 km\r\naltitudes. Deep in the warm troposphere the contribution of water to refractivity becomes\r\nsufficiently large for the accurate retrieval of water vapor given independent temperatures\r\nfrom weather analyses. We discuss several applications of the unique qualities of the\r\ntechnique including numerical weather prediction and long term monitoring of Earth's\r\nclimate.
\r\n\r\nThe second goal is to demonstrate some features using data from the prototype\r\nGPS-MET occultation investigation. We demonstrate ~1 km vertical resolution and\r\ntemperature consistency with global weather analyses generally at the 0.5 to 1 K level.\r\nWe discuss some initial observations of equatorial waves in the lower stratosphere and\r\npossible implications for exchange between the troposphere and stratosphere. During the\r\nJune-July 1995 period, occultations typically extend to within 1 to 3 km of the surface and\r\nare used to derive a brief climatology of water vapor in latitude versus height, the first\r\ntruly global view of water vapor at ~1 km vertical resolution. A low latitude bias structure\r\nin the weather analyses is revealed centered near 2 km altitude where analysis humidities\r\nare larger than those derived from the occultations in the subtropics but smaller in the\r\ntropics apparently associated with a systematic error in the boundary layer height in the\r\nanalyses.
", "doi": "10.7907/HPMZ-6524", "publication_date": "1997", "thesis_type": "phd", "thesis_year": "1997" }, { "id": "thesis:5736", "collection": "thesis", "collection_id": "5736", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:04222010-100328955", "primary_object_url": { "basename": "Haldemenn_afc_1997.pdf", "content": "final", "filesize": 37232907, "license": "other", "mime_type": "application/pdf", "url": "/5736/1/Haldemenn_afc_1997.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "Interpreting Radar Scattering: Circular-Polarization Perspectives from Three Terrestrial Planets", "author": [ { "family_name": "Haldemann", "given_name": "Albert Frank Christian", "clpid": "Haldemann-Albert-Frank-Christian" } ], "thesis_advisor": [ { "family_name": "Muhleman", "given_name": "Duane Owen", "clpid": "Muhleman-D-O" }, { "family_name": "Murray", "given_name": "Bruce C.", "clpid": "Murray-B-C" } ], "thesis_committee": [ { "family_name": "Murray", "given_name": "Bruce C.", "clpid": "Murray-B-C" }, { "family_name": "Albee", "given_name": "Arden Leroy", "clpid": "Albee-A-L" }, { "family_name": "Ingersoll", "given_name": "Andrew P.", "clpid": "Ingersoll-A-P" }, { "family_name": "Kamb", "given_name": "W. Barclay", "clpid": "Kamb-W-B" }, { "family_name": "Muhleman", "given_name": "Duane Owen", "clpid": "Muhleman-D-O" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "Planetary radar astronomy has used circular polarization radar signals to probe the surfaces of many solar system targets. However the trend for terrestrial observations has been toward greater use of linearly polarized imaging radars. Fortunately the latest generation of imaging radars has been developed with a multi-polarization capability. This should allow a synergy of the two research communities to occur.
\r\n\r\nOne of the unresolved debates on planetary radar astronomy is the nature of the scattering processes from cold planetary ices. This question recently received input from a terrestrial source: Greenland (Rignot et al. 1993). In this thesis a survey is made of high altitude sites to discover if the Greenland percolation zone scattering behavior is wide-spread on the Earth. The survey was carried out with the enormous, publicly available dataset from the 1994 missions of Shuttle Imaging Radar payload. This instrument (SIR-C) obtained full-polarization information with its linear-polarization system. These data allow reconstruction of circular polarizations for comparison to planetary results. The search proved fruitful. Hundreds of square kilometers in western Tibet's Kunlun Shan, and in the Central Andes at the latitude of Santiago display radar scattering behavior quite similar to that in Greenland where internal reflections of the radar waves within icy inclusions in the firn enhance scattering in the same sense of circular polarization.
\r\n\r\nA separate unresolved issue in the planetary radar astronomy is the question of the nature of the highlands of Venus that exhibit high radar reflectivity and low emissivity. These so-called anomalous radar behavior in these regions have alternately been ascribed to high-dielectric doping or low dielectric volume scatterinig. We present new dual circular-polarization radar maps of the western hemisphere of Venus. The results are from a 1993 experiment to image Venus with 3.5 cm radar. Maps of Venusian radar albedo were made for each of two days of observation in both OS (echo principally due to specular reflection) and SS (diffuse echo) channels. On both days, the sub-earth longitude was near 300E. The SS maps are dominated by a significant component of diffuse backscatter from the 285E longitude highlands: Beta, Phoebe, and Themis Regiones. Beta Regio includes previously observed radar-anomalous regions. The nature of these altitude-related electrical properties on Venus is one of the outstanding surface process questions that remain after the Magellan mission. Our experiment provides the first full-disk polarization ratio (\u00b5_c) maps. The data show that different geology determines different radar scattering properties within Beta. Diffuse scattering is very important in Beta, and may be due to either surface or volume scattering. We find a strong correlation of the SS albedo \u03c3_(SS) with altitude R_p (km) in Beta, \u03c3_(SS) \u221d0.3R_p. Also, \u03c3_(OS) \u221d0.7 R_p. The onset of this relationship is at the R_p~6054 km planetary radius contour. The nature and morphology of the highland radar anomalies in Beta is consistent with a diffuse scattering mechanism. In Beta Regio we find \u00b5_c > 0.5 in general, with \u00b5_c as high as 0.8 between Rhea and Theia Montes, to the west of Devana Chasma. These values are compatible with measurements of blocky terrestrial lava flows if surface scattering dominates. If volume scattering is important, the high RCP cross-sections may indicate an important decrease in embedded scatterer size with altitude, which could be related to enhanced weathering.
\r\n\r\nFinally, the techniques of planetary radar astronomy were used in an applied sense. Results are presented of 3.5-cm delay-Doppler and Doppler-only (continuous wave or CW) radar experiments to assess three potential Mars Pathfinder landing sites: Ares Vallis, Tritonis Lacus, and northwest (NW) Isidis. The regional relief at all of the landing sites is appropriate for a Pathfinder landing sequence: east-west slopes do not exceed 3\u00b0 at any of the sites. We find that Ares Vallis has a Hagfors rms slope of \u03b8_(rms)=4.8\u00b0\u00b11.1\u00b0 as measured by delay-Doppler radar, and \u03b8_(rms)=6.4\u00b0\u00b10.6\u00b0 measured by CW radar. These values are similar to, or less than the previous measurements of the Viking Lander 1 region (\u03b8_(rms)=6\u00b0, Tyler et al. 1976, Harmon 1997). The Tritonis Lacus landing site is rougher with delay- Doppler, \u03b8_(rms)=5.6\u00b0\u00b10.6\u00b0, while the NW Isidis landing site is very smooth, both in a regional sense (slopes < 0.7\u00b0) and in a Hagfors rms slope sense: \u03b8_(rms)=1.8\u00b0\u00b10.2\u00b0. Reflectivities at all of the sites should be sufficient to allow the radar altimeter on Pathfinder to function properly.
\r\n", "doi": "10.7907/YQ6F-ZS42", "publication_date": "1997", "thesis_type": "phd", "thesis_year": "1997" }, { "id": "thesis:7437", "collection": "thesis", "collection_id": "7437", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:01252013-094647944", "type": "thesis", "title": "Atmospheric chemistry in the outer solar system: from 40 K to 4000 K", "author": [ { "family_name": "Lyons", "given_name": "James Richard", "clpid": "Lyons-J-R" } ], "thesis_advisor": [ { "family_name": "Yung", "given_name": "Yuk L.", "clpid": "Yung-Y-L" } ], "thesis_committee": [ { "family_name": "Stevenson", "given_name": "David John", "clpid": "Stevenson-D-J" }, { "family_name": "Ingersoll", "given_name": "Andrew P.", "clpid": "Ingersoll-A-P" }, { "family_name": "Muhleman", "given_name": "Duane Owen", "clpid": "Muhleman-D-O" }, { "family_name": "Yung", "given_name": "Yuk L.", "clpid": "Yung-Y-L" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "This thesis consists of four papers on the general subject of atmospheric chemistry\r\nin the outer solar system. Although all are reducing environments, the atmospheres differ\r\nwidely in the ranges of temperature and pressure they encompass. Individual abstracts are\r\ngiven below.
\r\n\r\nPhotochemistry of the Atmosphere and Ionosphere of Triton
\r\n\r\nA one-dimensional photochemical model of the atmosphere and ionosphere of\r\nTriton was constructed to evaluate the significance of CO and CO_2, detected as surface\r\nices (Cruikshank et al. 1993), to the gas phase chemistry. For a CO mixing ratio of 10(^-4),\r\nconsistent with the observed fraction of CO ice, the model yields several interesting\r\nresults. Gas phase production of CO_2 is slow, but may, with the help of heterogeneous\r\nreactions on aerosols, be capable of producing a detectable layer of CO_2 ice over the age\r\nof the solar system; however, we consider this unlikely. Atomic nitrogen, produced in the\r\nionosphere, diffuses to the lower atmosphere and recombines to form N_2 in a cycle in\r\nwhich C acts as a catalyst. In a model with solar radiation only, the model predicts N\r\ndensities a factor of two smaller than reported by Krasnopolsky et al. (1993). Atomic\r\ncarbon is produced in the ionosphere primarily by dissociative recombination of CO^+. For\r\nan assumed rate coefficient for charge exchange from N_2^+ and CO^+ to C of 1x10^(-10) cm^3\r\nsec^(-1), Triton's ionosphere is dominated by C^+ and can be accounted for entirely by solar\r\nradiation. For a rate coefficient 10 times smaller, magnetospheric electron precipitation\r\nis needed to account for the observed electron density, but C^+ is still the principal ion.\r\nElectron precipitation is necessary to explain the observed N abundances. Measurements\r\nof the rate coefficients for ion-molecule reactions involving neutral C are needed.
\r\n\r\nMetal Ions in the Atmosphere of Neptune
\r\n\r\nMicrowave propagation experiments performed with Voyager 2 at Neptune\r\nrevealed sharp layers of electrons with densities \u223c10^4 cm^(-3) in Neptune's lower ionosphere.\r\nThese layers are reminiscent of terrestrial sporadic-E layers, and, when taken together\r\nwith data from the other giant planets, confirm the importance of the magnetic field in\r\nlayer formation. A photochemical model which incorporates species produced by\r\nmeteoroid ablation predicts that Mg^+ is the most likely metal comprising the layers,\r\nalthough laboratory data on the kinetics of metallic atoms and ions in reducing\r\nenvironments are lacking. The metal chemistry discussed here is directly relevant to the\r\nabundant metals observed at the impact site of the G fragment of Comet Shoemaker-Levy\r\n9 on Jupiter.
\r\n\r\nMeteoroidal Influx into the Upper Atmospheres of Uranus and Neptune
\r\n\r\nResults from a recent analysis of meteoroid ablation rates in the atmosphere of\r\nNeptune have been coupled with photochemical models of the upper atmospheres of\r\nNeptune and Uranus to yield estimates of stratospheric water profiles as a function of\r\nmeteoroid influx. Because water has never been detected in the upper atmospheres of the\r\ngiant planets, the tangential column opacities of the model water profiles were compared\r\nwith UV absorption measurements made by Voyager to determine maximum water\r\ninfluxes. For Uranus an upper limit is obtained which is consistent with an Oort-family\r\nparticle population, but not with a large population of planet-family dust particles. For\r\nNeptune the model water profile is strongly dependent on the still uncertain eddy\r\ncoefficient, making it difficult to rule out a large planet-family of IDP's. However, an IDP\r\npopulation sufficiently large to account for the CO observed in Neptune's atmosphere can\r\nbe ruled out.
\r\n\r\nA Chemical Kinetics Model for the Comet Impact with Jupiter
\r\n\r\nA chemical kinetics code was developed for gas phase species comprised of the\r\nelements H,C,N,O,S and Si. The code is valid at high temperatures and for H-dominated\r\ncompositions. The kinetics model was tested by running it to steady state equilibrium and\r\ncomparing the results with a thermochemical model. Model runs for pressure-temperature\r\nhistories relevant to the comet Shoemaker-Levy 9 impacts with Jupiter were made for\r\nC > O and C less than O compositions and for a variety of temperatures. Results indicate that the\r\nplume gas must have C > O, in agreement with Zahnle et al. (1995), implying a greater\r\nthan 50:1 mix of Jupiter gas to vaporized comet.
", "doi": "10.7907/D9MH-G975", "publication_date": "1996", "thesis_type": "phd", "thesis_year": "1996" }, { "id": "thesis:5658", "collection": "thesis", "collection_id": "5658", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:03302010-131151765", "primary_object_url": { "basename": "Gerstell_mf_1995.pdf", "content": "final", "filesize": 4399813, "license": "other", "mime_type": "application/pdf", "url": "/5658/1/Gerstell_mf_1995.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "Part 1. Two radiative transfer models with terrestial applications. Part 2. Testing the porcupine plate hypothesis", "author": [ { "family_name": "Gerstell", "given_name": "Marguerite F.", "clpid": "Gerstell-Marguerite-F" } ], "thesis_advisor": [ { "family_name": "Yung", "given_name": "Yuk L.", "orcid": "0000-0002-4263-2562", "clpid": "Yung-Y-L" } ], "thesis_committee": [ { "family_name": "Yung", "given_name": "Yuk L.", "orcid": "0000-0002-4263-2562", "clpid": "Yung-Y-L" }, { "family_name": "Ingersoll", "given_name": "Andrew P.", "orcid": "0000-0002-2035-9198", "clpid": "Ingersoll-A-P" }, { "family_name": "Muhleman", "given_name": "Duane Owen", "clpid": "Muhleman-D-O" }, { "family_name": "Stock", "given_name": "Joann M.", "orcid": "0000-0003-4816-7865", "clpid": "Stock-J-M" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "Paper I: Goody's convolution theorem for obtaining the cumulative k-distribution of a gas mixture requires stronger assumptions than the multiplicative property of band transmission; thus new experimental investigations of its effectiveness were undertaken. The convolution was found to be a useful speed optimization of k-distribution calculations at high pressures. For low pressures a variety of mixing methods were compared, all taking advantage of the idea that stratospheric lines are too narrow to overlap.\r\n\r\nAppendix I discusses the context and application of k-distribution calculations.\r\n\r\nPaper II: We used a \"quasi-random\" radiative transfer model to estimate stratospheric radiative perturbations produced by SO_2 gas, silicate ash, and H_2SO_4 aerosols after the 1982 El Chichon eruptions. One week after the last eruption, net radiative heating perturbations exceeding 20 K/day were modeled at altitudes near 26 km. Silicate ash heating may have been balanced by global enhancement of stratospheric meridional circulation, with upward velocities of 1 cm/s near Chichon's latitude. Radiative forcing by silicate ash and SO_2 gas should be included in more comprehensive models of plume evolution. Particle size distributions inferred from ash fallout rates could be wrong if radiative heating is neglected.\r\n\r\nPaper III: Uncertainties in the solar spectrum can affect modeled net heating rates in the upper stratosphere by a factor of several. Variation among Antarctic surface albedo values in common use can affect modeled net heating rates in the lower stratosphere by tens of percent. Large uncertainties in polar cloud cover are less important to stratospheric heating models. I join Marcel Nicolet in urging support for a continuous solar observation program, and recommend that future intercomparisons of stratospheric radiation models prescribe a solar spectrum, to reveal other differences.\r\n\r\nAppendix 2 gives the details of some further validation and sensitivity tests for the quasi-random model.\r\n\r\nPaper IV: The Porcupine Plate was postulated in 1986 to explain difficulties in reconstructing anomalies 21 and 24 in the North Atlantic. Its main feature was thought to be a transpressive Eocene plate boundary along Charlie-Gibbs Fracture Zone. Eliminating data that could have been affected by subsequent movements of Greenland relative to North America leads to a picture that casts doubt on the Porcupine Plate hypothesis.\r\n", "doi": "10.7907/e7ex-9x13", "publication_date": "1995", "thesis_type": "phd", "thesis_year": "1995" }, { "id": "thesis:4414", "collection": "thesis", "collection_id": "4414", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-11052007-080036", "primary_object_url": { "basename": "Stephens_sk_1995.pdf", "content": "final", "filesize": 8685339, "license": "other", "mime_type": "application/pdf", "url": "/4414/1/Stephens_sk_1995.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Carbonate formation on Mars : experiments and models", "author": [ { "family_name": "Stephens", "given_name": "Stuart Keller", "clpid": "Stephens-S-K" } ], "thesis_advisor": [ { "family_name": "Stevenson", "given_name": "David John", "clpid": "Stevenson-D-J" } ], "thesis_committee": [ { "family_name": "Stevenson", "given_name": "David John", "clpid": "Stevenson-D-J" }, { "family_name": "Ingersoll", "given_name": "Andrew P.", "clpid": "Ingersoll-A-P" }, { "family_name": "Murray", "given_name": "Bruce C.", "clpid": "Murray-B-C" }, { "family_name": "Muhleman", "given_name": "Duane Owen", "clpid": "Muhleman-D-O" }, { "family_name": "Rossman", "given_name": "George Robert", "clpid": "Rossman-G-R" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThe experiments reported in this thesis were motivated by a desire to explain the small present [...] pressure in the Martian atmosphere, given the hypothesis that Mars once possessed a much denser [...] atmosphere. We adopted the premise that carbonate production on the surfaces of regolith particles, mediated by small amounts of [...], might explain the decline in the surface pressure over geologic timescales.\r\n\r\n\tWe exposed powders [...] of basalt glass, and of monominerallic diopside, olivine, plagioclase, and quartz, to conditions simulating the past and present surface of Mars ([...], and [...] contents equivalent to <1 to >5000 monolayers on particle surfaces). A sensitive manometer was used to acquire precise measurements of pressure over periods of [...] days. Initial pressure drops were attributed to adsorption of [...] on particle surfaces and dissolution of [...]. Continuing uptake of gas in most experiments suggested that [...] reacted with powders to form carbonate. Fits to [...] after [...] day gave [...], implying logarithmic reaction kinetics (i.e., reaction rate, [...]. Subsequent fits to [...], incorporating adsorption and dissolution, gave rates of D = 0.01-2 monolayers [...] per [...], with [...] day. Reaction amounts totaled [...] monolayers. Parabolic kinetics, arising from diffusion through a product layer, probably did not exceed P(t) [...]\r\n\r\nRates varied with sample composition (basalt and diopside > olivine > plagioclase and quartz). Basalt glass was not more reactive than diopside. Basalt powder pretreated with weak acid displayed rates reduced by over an order of magnitude (although diopside did not), suggesting something removed by acid contributes to [...] uptake. Rates increased with [...] content, temperature, and CO2 pressure, vA fit to data for basalt at 295 K gave [...], where H is [...] content in monolayers and D is in monolayers [...] per log [...]t; at 248-263 K, the-effect of [...] is stronger: [...]. [...] for \"dry\" experiments; no lower limit was put on [...] required for reaction.\r\n\r\nReflectance spectra at mid-infrared wavelengths [...] were obtained for all \"dry\" and \"vapor\" experimental powders, and ratioed to starting spectra for maximum sensitivity to added phases. Prominent spectral features near [...] in basalt and diopside coincided with [...] absorptions at 6.9 [...] for calcite. Additional absorptions near 6.1 [...] in basalt and 4.0 [...] in diopside were also consistent with the presence of calcite. Absorption ratios near 7 [...] ranged from [...] (corresponding to perhaps 3 wt% added calcite) to as little as [...], below which we were unable to identify added phases. There was a clear positive correlation between absorption ratios and experimental [...] uptakes (and hence [...] content), strengthening the conclusion that carbonate--probably calcite but perhaps magnesite or dolomite--formed in pressure-drop experiments.\r\n\r\nOur experiments suggested that this process does occur, but modeling and application to Mars indicated that it may be insufficient to explain the carbonate production required to reduce atmospheric pressure by [...] bar over geologic time. The principal difficulty lies in the lack of evidence for the reaction proceeding easily beyond one monolayer of product. Although some experiments displayed evidence for the growth of more than a monolayer, they also showed that this arises in a regime of logarithmic reaction kinetics, where [...] uptake is limited by declining surface area available for reaction. For a global layer of basalt powder, only high specific surface area [...], a deep regolith (>100 m), or plentiful [...] (equivalent to films >5 monolayers thick) allow total [...] stored as carbonate to exceed [...] mb. Diffusion-limited kinetics were not ruled out for timescales much longer than experimental durations, and models with thicker carbonate growths show that this could account for storage of an early Martian atmosphere.\r\n\r\nOther mechanisms for the loss of [...] may also contribute in the transition to the present surface pressure. Or, Mars may simply never have had a dense, [...] atmosphere, although this requires explanations other than a [...] greenhouse for the morphological features used to support the hypothesis of a warm, wet early Mars. If large amounts of carbonate minerals do represent a sink for atmospheric [...], the question of their location on the surface still remains since they have not been confirmed spectroscopically.\r\n", "doi": "10.7907/PSFY-MZ22", "publication_date": "1995", "thesis_type": "phd", "thesis_year": "1995" }, { "id": "thesis:4423", "collection": "thesis", "collection_id": "4423", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-11062007-083125", "primary_object_url": { "basename": "Ray_tw_1995.pdf", "content": "final", "filesize": 60568633, "license": "other", "mime_type": "application/pdf", "url": "/4423/1/Ray_tw_1995.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Remote monitoring of land degradation in arid/semiarid regions", "author": [ { "family_name": "Ray", "given_name": "Terrill Wylie", "clpid": "Ray-T-W" } ], "thesis_advisor": [ { "family_name": "Murray", "given_name": "Bruce C.", "clpid": "Murray-B-C" } ], "thesis_committee": [ { "family_name": "Murray", "given_name": "Bruce C.", "clpid": "Murray-B-C" }, { "family_name": "Albee", "given_name": "Arden Leroy", "clpid": "Albee-A-L" }, { "family_name": "Anderson", "given_name": "Donald L.", "clpid": "Anderson-D-L" }, { "family_name": "Muhleman", "given_name": "Duane Owen", "clpid": "Muhleman-D-O" }, { "family_name": "Wyllie", "given_name": "Peter J.", "clpid": "Wyllie-P-J" }, { "family_name": "Blom", "given_name": "Ron", "clpid": "Blom-R" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nLand degradation is a serious and growing problem on a world-wide scale -- 11% of the Earth's vegetated surface having suffered serious damage in the last 45 years. Human activity, especially sprinkler irrigation agriculture, can cause dramatic changes in arid regions as the fragile natural plant cover is stripped off and its root system destroyed in the process of cultivation. Satellite and airborne remote sensing data covering the Manix Basin of Eastern California over the last two decades shows that abandoned fields there suffered progressive degradation, as the topsoil eroded due to the lack of protective plant cover. Blowing sand buried and disrupted the downwind plant cover, which caused the downwind area to lose its protection against wind erosion and expanded the region of damage.\r\n\r\nBecause the amount and kind of plant cover is an important marker both of where wind erosion has occurred and where it is likely to occur in the future, especially designed satellite monitoring systems should be able to sense to signatures of undisturbed and disturbed vegetation cover in arid regions. However, this problem cannot be addressed by standard vegetation indices, because of the adaptation of arid region plants to the scarcity of water. Furthermore, weekly to monthly sampling will be necessary because blowing sand visible to satellite remote sensing is highly dependent on the local weather, and this can change within a few months. A new vegetative index suitable for arid regions is proposed for the wavelength region from 0.4-1.0 [...].\r\n\r\nThe detection and identification of arid region plant communities requires a highly calibrated remote sensing system with higher spectral resolution than that currently offered by Landsat Thematic Mapper. The way in which regions of blowing sand can appear and disappear with rapidity demonstrates the need for a remote monitoring system that can survey large areas on a regular basis. Such a system must be supported by focused ground observations and a continuing analysis of the satellite data.\r\n", "doi": "10.7907/65EA-Y568", "publication_date": "1995", "thesis_type": "phd", "thesis_year": "1995" }, { "id": "thesis:4346", "collection": "thesis", "collection_id": "4346", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-10312007-094538", "primary_object_url": { "basename": "McMuldroch_s_1995.pdf", "content": "final", "filesize": 6352429, "license": "other", "mime_type": "application/pdf", "url": "/4346/1/McMuldroch_s_1995.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "The Circumstellar Environments of FU Orionis Stars", "author": [ { "family_name": "McMuldroch", "given_name": "Stuart", "clpid": "McMuldroch-Stuart" } ], "thesis_advisor": [ { "family_name": "Sargent", "given_name": "Anneila Isabel", "orcid": "0000-0002-4633-5098", "clpid": "Sargent-A-I" }, { "family_name": "Blake", "given_name": "Geoffrey A.", "orcid": "0000-0003-0787-1610", "clpid": "Blake-G-A" } ], "thesis_committee": [ { "family_name": "Westphal", "given_name": "James A.", "clpid": "Westphal-J-A" }, { "family_name": "Blake", "given_name": "Geoffrey A.", "orcid": "0000-0003-0787-1610", "clpid": "Blake-G-A" }, { "family_name": "Burnett", "given_name": "Donald S.", "clpid": "Burnett-D-S" }, { "family_name": "Sargent", "given_name": "Anneila Isabel", "orcid": "0000-0002-4633-5098", "clpid": "Sargent-A-I" }, { "family_name": "Muhleman", "given_name": "Duane Owen", "clpid": "Muhleman-D-O" } ], "local_group": [ { "literal": "Astronomy Department" }, { "literal": "div_gps" } ], "abstract": "Extensive observations were made of six FU Orionis objects (RNO 1B/1C, V1057 Cygni, Elias 1-12, V1515 Cygni and FU Orionis) and one pre-outburst candidate (V1331 Cygni) using the Owens Valley millimeter-wave array and the Caltech Submillimeter Observatory (CSO). Aperture synthesis maps of CO (1\u21920), \u00b9\u00b3CO (1\u21920), \u00b9\u00b3CO (2\u21921), \u00b9\u2078CO (1\u21920), and \u00b3CO (2\u21921) molecular lines and associated dust continuum emission trace the masses, kinematics and morphology of FU Orionis disks, envelopes, and outflows. Maps from the CSO delineate outflowing gas at larger spatial scales while line strengths, when input into radiative transfer models, yield column densities and fractional chemical abundances.
\r\n\r\nUnresolved 1.3 mm continuum emission from Vl331 Cygni and V1057 Cygni reveal massive circumstellar disks of 0.5 and 0.09 M\u2609, respectively. Maps of the 2.6 and 3.1 mm continuum emission reveal that RNO 1C is surrounded by a flattened dusty envelope, 5000 AU in size, with mass \u2a7e 1.1 M\u2609. No evidence is seen for multiple systems with orbital periods \u2273 4 x 10\u2074 years years.\r\n\r\nAll sources, with the exception of RNO 1B/1C are surrounded by large molecular gas envelopes between 2000-7500 AU in size, with masses ranging from 2 x 10\u207b\u00b3 to 0.36 M\u2609. Aperture synthesis maps suggest the envelopes are asymmetrically distributed. Gas kinematics around V1057 Cygni and Elias 1-12 suggest, but do not demand, that this material is rotating and possibly infalling.
\r\n\r\nOf the seven sources observed, all but FU Orionis show signs of outflowing molecular gas. No high velocity clumps or \"bullets\" are seen towards any of the sources. V1331 Cygni, V1057 Cygni, and V1515 Cygni possess arc or ring-like outflow morphologies, while emission from RNO 1B/1C and Elias 1-12 delineates filled outflow shells. All emission patterns are consistent with outflow shells being viewed at different angles. Although based on the statistics of small numbers, observations suggest shells are seen more frequently around FUors than T Tauri stars. Shell formation may therefore be caused by time-dependent events in the outflow. Cross-cutting arcs within the shell structure, seen towards RNO 1B/1C and Elias 1-12, are probably ridges of gas swept-up by the most recent outbursts, confirming the repetitive nature of FUor outbursts. Estimates of the dynamical ages of the arcs suggest that the interval between outbursts is ~5 x 10\u00b3 and 1.3 x 10\u2074 years for RNO 1B/1C and Elias 1-12 respectively, consistent with previous estimates of FUor cycling times.
\r\n\r\nComparable envelopes and shell-like outflow structure are seen towards embedded sources while envelopes surrounding T Tauri stars are smaller and less massive. This suggests FU Orionis objects are transition sources between deeply embedded and optically visible stars. The strength of the molecular outflow emission is correlated with the mass of the extended envelope; the outflow has evacuated molecular gas leaving less to be swept-up by subsequent outbursts, while envelope masses are smaller since less material is available for accretion.
\r\n\r\nChemically, fractional abundances of SiO and methanol are enhanced towards RNO 1B/1C by over an order of magnitude. Methanol is enhanced relative to HCN and H2CO towards Elias 1-12. Such large changes in fractional abundances must be caused by chemical processing. The SiO enrichments may be produced by sputtering or evaporation of dust grains in regions of directly shocked material or by chemical reactions of SiH4 after sublimation from grain surfaces. Methanol enrichments are difficult to produce in strong shocks, and may be caused by low velocity grain-grain collisions. For RNO 1B/1C, evaporation of the entire methanol rich grain mantles seems to be required; while for Elias 1-12 mantle phase changes from an amorphous ice to a clathrate hydrate can be invoked, expelling the methanol, with smaller molecules remaining trapped in the clathrate. Such low velocity collisions probably occur in the turbulent shear zones surrounding the outflowing gas.
", "doi": "10.7907/14NE-ZW09", "publication_date": "1995", "thesis_type": "phd", "thesis_year": "1995" }, { "id": "thesis:7472", "collection": "thesis", "collection_id": "7472", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:02112013-110255064", "primary_object_url": { "basename": "Betts 1994.pdf", "content": "final", "filesize": 50949690, "license": "other", "mime_type": "application/pdf", "url": "/7472/1/Betts 1994.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Thermal and visible studies of Mars using the Termoskan data set", "author": [ { "family_name": "Betts", "given_name": "Bruce Harold", "clpid": "Betts-B-H" } ], "thesis_advisor": [ { "family_name": "Murray", "given_name": "Bruce C.", "clpid": "Murray-B-C" } ], "thesis_committee": [ { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" }, { "family_name": "Ingersoll", "given_name": "Andrew P.", "clpid": "Ingersoll-A-P" }, { "family_name": "Muhleman", "given_name": "Duane Owen", "clpid": "Muhleman-D-O" }, { "family_name": "Murray", "given_name": "Bruce C.", "clpid": "Murray-B-C" }, { "family_name": "Paige", "given_name": "David", "clpid": "Paige-P" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "In February and March, 1989, the Termoskan instrument on board the Phobos '88\r\nspacecraft of the USSR acquired the highest spatial resolution thermal data ever obtained\r\nfor Mars, ranging in resolution from 300 m to 3 km per pixel. It simultaneously obtained\r\nbroad band visible channel data. The panoramas cover a large portion of the equatorial\r\nregion from 30\u00b0S to 6\u00b0N. New and unique analyses facilitated by Termoskan are\r\npresented here. In addition, this thesis describes the instrument, data, and validation.\r\nTermoskan thermal data shows good temperature agreement with Viking IRTM.\r\nHowever, conversion of Termoskan visible data to bolometric albedo is problematic.
\r\n\r\nUtilizing the Termoskan data, I recognized a new feature on Mars: ejecta blanket\r\ndistinct in the thermal infrared (EDITH). Virtually all of the more than 100 such features\r\ndiscovered in the Termoskan data are located on the plains near Valles Marineris. I\r\ncompiled a data base of 110 EDITH and non-EDITH craters ranging in diameter from 4.2\r\nkm to 90.6 km. EDITHs have a startlingly clear dependence upon terrains of Hesperian\r\nage, and show almost no other correlations within the data base. The Hesperian terrain\r\ndependence cannot be explained by either atmospheric or impactor variations. Wind\r\npatterns or locally available aeolian material cannot provide a single overall explanation for\r\nthe observed variations. I postulate that most of the observed EDITHs are due to\r\nexcavation of thermally distinctive Noachian age material from beneath a relatively thin\r\nlayer of younger, more consolidated Hesperian volcanic material. The plausibility of this\r\ntheory is supported by much geological evidence for relatively thin near-surface Hesperian\r\ndeposits overlying massive Noachian megabreccias on the EDITH-rich plains units. I\r\nsuggest that absence of thermally distinct ejecta blankets on Noachian and Amazonian\r\nterrains is due to absences of distinctive near-surface layering. Thermally distinct ejecta blankets are excellent locations for future landers and remote sensing because of relatively dust free surface exposures of material excavated from depth.
\r\n\r\nAlso included in the thermal images are observations of several major channel and\r\nvalley systems including significant portions of Shalbatana, Ravi, Al-Qahira, and Ma'adim\r\nValles, the channel south of Hydraotes Chaos, channel material in Eos Chasma, and small\r\nportions Simud, Tiu, and Ares Valles and channel material in Gangis Chasma.\r\nSimultaneous broad band visible data exists for all but Ma'adim Vallis. I find that most of\r\nthe channels and valleys have higher inertias than their surroundings, consistent with\r\nprevious thermal studies of martian channels. I show for the first time that thermal inertia\r\nboundaries closely match all flat channel floor boundaries. Using Viking albedos,\r\nTermoskan temperatures, and thermal modelling, I derive lower bounds on typical channel\r\nthermal inertias ranging from 8.4 to 12.5 (10^(-3) cal cm^(-2) s^(-1/2) K^(-1). Lower bounds on\r\ninertia differences with the surrounding heavily cratered plains range from 1.1 to 3.5.\r\nAtmospheric and geometric effects are not sufficient to cause the inertia enhancements. I\r\nagree with previous researchers that localized, dark, high inertia areas within channels are\r\nlikely aeolian in nature. However, thermal homogeneity and strong correlation of thermal\r\nboundaries with the channel floor boundaries lead me to favor non-aeolian overall\r\nexplanations. Small scale aeolian deposition or aeolian deflation may, however, play some\r\nrole in the inertia enhancement Channel floor inertia enhancements are strongly\r\nassociated with channels showing fretted morphologies such as wide, flat floors and steep\r\nscalloped walls. Therefore, I favor fretting processes over catastrophic flooding for\r\nexplaining the inertia enhancements. Fretting may have emplaced more blocks on channel\r\nfloors or caused increased bonding of fines due to increased availability of water.\r\nAlternatively, post-channel formation water that may have been preferentially present due\r\nto the low, flat fretted floors may have enhanced bonding of original fines or dust fallout\r\nThe coupling of both EDITHs and channel inertias to morphology is unlike most sharp\r\nMartian inertia variations which are decoupled from observed surface morphology.
\r\n\r\nTermoskan observed morning limb brightening in the thermal channel, but not in\r\nthe visible channel. The thermal morning limb brightening is likely due to a water ice or\r\ndust haze that is warmer than the surface at the time of the observations. A water ice haze\r\nwith a scale height of 5 km could match the observations. Visible scattering is observed to\r\nbe significant on morning and evening limbs out to 60 or 70 km. Localized high altitude\r\nstratospheric clouds are observed in the visible channel.
\r\n\r\nThe Termoskan data show that the highland-lowland boundary in the Aeolis\r\nQuadrangle appears strongly correlated with a high-low thermal inertia boundary. The\r\nsharpness of that boundary varies from less than 4 km to more than 50 km. In all cases,\r\ninertias continue to decrease gradually for many tens of km into the lowlands. Several\r\nother large scale thermal boundaries are also observed in the data.
\r\n\r\nTermoskan observed fine thermal structure on the flanks of Arsia Mons and\r\nelsewhere, which represent examples of interesting and significant thermal variations seen\r\nat the limit of Termoskan's spatial resolution. Sharp variations and boundaries imply there\r\ncannot be global scale dust blanketing deeper than about one centimeter, if that.
\r\n\r\nTermoskan obtained the first ever thermal images of Phobos' shadow on the\r\nsurface of Mars, along with simultaneous visible images. The best observed shadow\r\noccurrence was on the flanks of Arsia Mons. For this occurrence, I combined the\r\nobserved decrease in visible illumination of the surface with the observed decrease in\r\nbrightness temperature to calculate thermal inertias of the Martian surface. Most of the\r\nderived inertias fall within the range 0.9 to 1.4, corresponding to 5 to 10 micron dust\r\nparticles for a homogeneous surface. Dust at the surface is consistent with previous\r\ntheories of Tharsis as a current area of dust deposition. Shadow derived inertias are\r\nsensitive to mm depths, whereas diurnally derived inertias are sensitive to cm depths. The\r\nshadow derived inertias are very similar to Haberle and Jakosky [1991] atmospherically\r\ncorrected Palluconi and Kieffer [1981] Viking IRTM diurnally derived inertias. Thus, if\r\nnear surface layering exists at all in this region, it is not very significant.
\r\n\r\n\r\n", "doi": "10.7907/M9T5-G181", "publication_date": "1994", "thesis_type": "phd", "thesis_year": "1994" }, { "id": "thesis:933", "collection": "thesis", "collection_id": "933", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-03112009-141429", "primary_object_url": { "basename": "Svitek_t_1992.pdf", "content": "final", "filesize": 9657969, "license": "other", "mime_type": "application/pdf", "url": "/933/1/Svitek_t_1992.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Martian water frost : control of global distribution by small-scale processes", "author": [ { "family_name": "Svitek", "given_name": "Tomas", "clpid": "Svitek-T" } ], "thesis_advisor": [ { "family_name": "Murray", "given_name": "Bruce C.", "clpid": "Murray-B-C" } ], "thesis_committee": [ { "family_name": "Murray", "given_name": "Bruce C.", "clpid": "Murray-B-C" }, { "family_name": "Ingersoll", "given_name": "Andrew P.", "clpid": "Ingersoll-A-P" }, { "family_name": "Albee", "given_name": "Arden Leroy", "clpid": "Albee-A-L" }, { "family_name": "Kamb", "given_name": "W. Barclay", "clpid": "Kamb-W-B" }, { "family_name": "Stevenson", "given_name": "David John", "clpid": "Stevenson-D-J" }, { "family_name": "Muhleman", "given_name": "Duane Owen", "clpid": "Muhleman-D-O" }, { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" }, { "family_name": "Yung", "given_name": "Yuk L.", "clpid": "Yung-Y-L" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "This thesis analyzes the small\u2014scale physical processes occurring in the Martian water polar frosts. The small\u2014scale processes are considered from the point of view of how they control the global distribution and behavior of water on Mars. The analysis of the small\u2014scale properties of the surface frost is essential in efforts to find solutions for some outstanding, contradictory observations, to interpret correctly remote sensing observations, to model the surface\u2014frost thermal balance, and to implement the boundary conditions and parameterizations used in the global models of the volatiles' behavior on Mars. Two different problems are investigated in this thesis:\r\n\r\nThe effect of surface roughness on frost temperature and morphology is studied in Chapter 2 and 3. The investigation of the temperature/roughness feedback leads to the following suggestion: There is a natural tendency of volatile surfaces to develop spontaneously small-scale roughness in a sublimation\u2014dominated environment. The evidence for this claim consists of the model of a rough\u2014surface thermal balance, and of the terrestrial analogs of differential sublimation structures. Such a phenomenon can be tested by the Mars Observer and has important implications for the behavior of water frost on Mars.\r\n\r\nViking Lander 2 winter\u2014frost observations are described in Chapter 4. This study suggests that winter water frost occurred there in two forms: a) thin, almost continuous, early frost, and b) much thicker, patchy, later frost with local cold\u2014trapping of water vapor playing the crucial role. This conclusion is based on the correlation of multiple data sets (from both Viking Orbiter and Lander) and on the combined models of the physical processes occurring on a small scale \u2014 below the resolution of remote sensing. The evidence consists of the frost\u2014surface coverage and color transitions, and of the calculation of the vertical and horizontal water\u2014vapor transport near the surface. Again, this phenomenon can be confirmed or rejected by a set of observations from the Mars Observer.\r\n\r\nThe inherent rough\u2014surface morphology and the frost cold\u2014trapping must be a general property of at least some forms of the seasonal and residual frosts. Both effects must be considered in order to understand the global observations of the Martian frost and the surface environment of Mars in general.\r\n", "doi": "10.7907/EDK8-3457", "publication_date": "1992", "thesis_type": "phd", "thesis_year": "1992" }, { "id": "thesis:2550", "collection": "thesis", "collection_id": "2550", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-06112007-132024", "type": "thesis", "title": "I. Impact of Volcanic Aerosols on Stratospheric Chemistry. II. O\u2082(\u00b9\u03a3g\u207a) and O\u2082(\u00b9\u0394g\u207a) in the H + O\u2082 Reaction System. III. Barotropic Instability of Zonal Jets on Mars, Earth and Venus", "author": [ { "family_name": "Michelangeli", "given_name": "Diane Vera", "clpid": "Michelangeli-Diane-Vera" } ], "thesis_advisor": [ { "family_name": "Yung", "given_name": "Yuk L.", "orcid": "0000-0002-4263-2562", "clpid": "Yung-Y-L" }, { "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": "Blake", "given_name": "Geoffrey A.", "orcid": "0000-0003-0787-1610", "clpid": "Blake-G-A" }, { "family_name": "Muhleman", "given_name": "Duane Owen", "clpid": "Muhleman-D-O" }, { "family_name": "Leu", "given_name": "Ming-Taun", "clpid": "Leu-Ming-Taun" }, { "family_name": "Yung", "given_name": "Yuk L.", "orcid": "0000-0002-4263-2562", "clpid": "Yung-Y-L" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "In order to fully understand an atmospheric system, we must answer questions in radiative transfer (Paper I), dynamics (Paper II), and chemistry (Paper I). The adequacy of the chemical models at reproducing the atmosphere depends on the fundamental knowledge of rate constants and absorption cross sections, which are determined in laboratory experiments (Paper III). All these issues are investigated in the three independent papers of this thesis. While seemingly unrelated, they all attempt to explain observations of terrestrial atmospheres. Paper I focuses on the chemical effects, in the Earth's stratosphere, of a volcanic eruption. Paper II reports experimental results important for the understanding of nightglow emissions on Earth. And finally, Paper III discusses barotropic instabilities as a possible explanation for thermal waves on Mars.
", "doi": "10.7907/6s4a-6e87", "publication_date": "1989", "thesis_type": "phd", "thesis_year": "1989" }, { "id": "thesis:2308", "collection": "thesis", "collection_id": "2308", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-05302007-084208", "type": "thesis", "title": "A Dynamical Study of Jupiter's Great Red Spot", "author": [ { "family_name": "Dowling", "given_name": "Timothy Edward", "clpid": "Dowling-Timothy-Edward" } ], "thesis_advisor": [ { "family_name": "Ingersoll", "given_name": "Andrew P.", "orcid": "0000-0002-2035-9198", "clpid": "Ingersoll-A-P" }, { "family_name": "Muhleman", "given_name": "Duane Owen", "clpid": "Muhleman-D-O" } ], "thesis_committee": [ { "family_name": "Muhleman", "given_name": "Duane Owen", "clpid": "Muhleman-D-O" }, { "family_name": "Ingersoll", "given_name": "Andrew P.", "orcid": "0000-0002-2035-9198", "clpid": "Ingersoll-A-P" }, { "family_name": "Leonard", "given_name": "Anthony", "clpid": "Leonard-A" }, { "family_name": "Stevenson", "given_name": "David John", "clpid": "Stevenson-D-J" }, { "family_name": "Zurek", "given_name": "Richard W.", "clpid": "Zurek-Richard-W" } ], "local_group": [ { "literal": "Astronomy Department" }, { "literal": "div_gps" } ], "abstract": "This work is presented in the form of two related papers. In the first paper we investigate layer thickness variations in Jupiter's atmosphere by tracking absolute vorticity (\u03b6 + f) along streamlines of the Great Red Spot (GRS) and White Oval BC. The ratio of absolute vorticity to layer thickness, called the potential vorticity, is conserved following the motion. By observing Lagrangian variations of absolute vorticity, we may infer variations in layer thickness. The data thus obtained are a useful diagnostic that will help differentiate between models of Jovian vortices. We interpret the observed layer thickness variations using a simple \"1-1/2\" layer model in which a thin upper weather layer, which contains the vortices, overlies a much deeper layer, which is meant to model the deep atmosphere. In this model, layer thickness variations are directly coupled to motions in the deep atmosphere, and we use the data to infer the deep motions. In the first paper we interpret the data, using the quasi-geostrophic equations. In the second paper we reinterpret the data, using the more general shallow water equations. Most current models of the GRS are cast in terms of the 1-1/2 layer model, and they start by prescribing the motions in the deep atmosphere. Here we are able to derive the deep motions using the same 1-1/2 layer model assumptions, up to a constant that depends on the unknown static stability of Jupiter's troposphere. None of the current prescriptions for the deep motions are in qualitative agreement with the observations over the full range of latitudes observed. We study the 1-1/2 layer model numerically, using both the derived deep motions and the prescribed deep motions of current models. Only the present model, based on observations, yields Lagrangian absolute vorticity profiles that agree with those obtained in the first paper. A model run that starts with the observed zonally averaged cloud-top winds and derived deep motions shows instability, which naturally leads to the genesis and maintenance of a large, isolated vortex similar to the GRS.
", "doi": "10.7907/whc3-mh91", "publication_date": "1989", "thesis_type": "phd", "thesis_year": "1989" }, { "id": "thesis:7484", "collection": "thesis", "collection_id": "7484", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:02202013-103037890", "primary_object_url": { "basename": "Rudy 1987.pdf", "content": "final", "filesize": 28898031, "license": "other", "mime_type": "application/pdf", "url": "/7484/1/Rudy 1987.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Mars: High Resolution VLA Observations at Wavelengths of 2 and 6 cm and Derived Properties", "author": [ { "family_name": "Rudy", "given_name": "Donald James", "clpid": "Rudy-Donald-James" } ], "thesis_advisor": [ { "family_name": "Ingersoll", "given_name": "Andrew P.", "clpid": "Ingersoll-A-P" } ], "thesis_committee": [ { "family_name": "Ingersoll", "given_name": "Andrew P.", "clpid": "Ingersoll-A-P" }, { "family_name": "Albee", "given_name": "Arden Leroy", "clpid": "Albee-A-L" }, { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" }, { "family_name": "Murray", "given_name": "Bruce C.", "clpid": "Murray-B-C" }, { "family_name": "Muhleman", "given_name": "Duane Owen", "clpid": "Muhleman-D-O" } ], "local_group": [ { "literal": "Astronomy Department" }, { "literal": "div_gps" } ], "abstract": "Observations of Mars at wavelengths of 2 and 6cm were made using the VLA in its A configuration. Two seasons were observed; late spring in the northern hemisphere (LS ~ 60\u00b0) and early summer in the southern summer (LS ~ 300\u00b0). The sub-earth latitudes were 25\u00b0N and 25\u00b0S, for each of these seasons respectively. So the geometry for viewing the polar region was optimal in each case. Whole-disk brightness temperatures were estimated to be 193.2 K \u00b1 1.0 at 2 cm and 191.2 K \u00b1 0.6 at 6 cm for the northern data set and 202.2 K \u00b1 l.0 at 2 cm and 195.4 K \u00b1 0.6 at 6 cm for the southern data set (formal errors only). Since measurements of the polarized flux were taken at the same time, whole-disk effective dielectric constants could be estimated and from these, estimates of sub-surface densities could be made. The results of these calculations at 2cm yielded whole-disk effective dielectric constants of 2.34 \u00b1 0.05 and 2.02 \u00b1 0.03 which imply sub-surface densities of 1.24 g cm-3 \u00b1 0.06 and 1.02 g cm-3 \u00b1 0.05 for the north and south, respectively. The same calculations at 6 cm yielded effective densities of 1.45 g cm-3 \u00b1 0.10 and 1.31 g cm-3 \u00b1 0.07 from effective dielectric constants of 2.70 \u00b1 0.09 and 2.48 \u00b1 0.06 for the north and south data sets, respectively.
\r\n\r\nFrom the mapped data these parameters were also estimated as a function of latitude between latitudes of 15\u00b0S and 60\u00b0N for the north data set; and between latitudes of 30\u00b0N and 60\u00b0S for the south data set. A region in which the brightness temperature behaves in an anomalous manner was discovered in both data sets. This region lies between about 10\u00b0S and 40\u00b0S. Here the brightness temperatures at both wavelengths in both data sets appears lower, by 4 K to 8 K, than a nominal model would predict. In addition to the effective dielectric constant and sub-surface density the radio absorption length of the sub-surface was estimated. The radio absorption length for most of these latitudes was about 15 wavelengths with formal errors on the order of 5 or 10 wavelengths. This is true for both data sets. The estimation of the effective dielectric constant at most latitudes was between 2 and 3.5 with only slight differences between the two different wavelengths. The two data sets show the same relative trends, but are off by a scaling factor.
\r\n\r\nThese estimates of the dielectric constant lead to estimation of the sub-surface densities as a function of latitude. Most calculations of the sub-surface density yielded results between 1 and 2 g cm-3 with errors on the order of 0.5 g cm-3. These results seem to imply that the sub-surface is not much different than the surface as observed by the Viking and Mariner missions. In line with this, an examination of the correlation of the dielectric constant at each wavelength with the thermal inertia, determined by the Viking infrared measurements, shows a relatively strong correlation, at both wavelengths, for the North data set. The South data set, however, shows little to nocorrelation between the radio parameters and the thermal inertia. Since the South data set is primarily composed of latitudes which contain the anomalous region, it is not suprising that the South data set shows no correlation.
\r\n\r\nIn addition, the thermal-radiative model used to estimate the above parameters was used to estimate the variability of the whole-disk brightness temperature of Mars. This was done in an effort to establish a background for those astronomers wishing to use Mars as a calibration source. The parameters investigated for their effect on the whole-disk brightness temperature of Mars were: the sub-earth longitude, the sub-earth latitude, the sub-earth time of day, the dielectric constant, and the radio absorption length. A nominal model was first created which established the variation of the brightness temperature as a function of season and radio absorption length. A nominal value of 2.2 was used for the dielectric constant, and the sub-earth latitude was set at 0\u00b0N and the sub-earth longitude was set at 75\u00b0W. The sub-earth time of day was held at noon for this nominal model. This is equivalent to a 0\u00b0 phase angle. The most important geometric factor was the sub-earth latitude. The error in estimating the whole-disk brightness temperature of Mars by using the wrong sub-earth latitude can be as large as 5 to 10%. The charts presented will be useful to estimate the whole-disk brightness temperature which the thermal model would predict. It is believed that the error in this estimate is less than or equal to 5 K.
\r\n", "doi": "10.7907/3g59-p796", "publication_date": "1987", "thesis_type": "phd", "thesis_year": "1987" }, { "id": "thesis:7452", "collection": "thesis", "collection_id": "7452", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:01292013-151449809", "primary_object_url": { "basename": "Friedson_aj_1987.pdf", "content": "final", "filesize": 33130951, "license": "other", "mime_type": "application/pdf", "url": "/7452/1/Friedson_aj_1987.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "I. Meridional Energy Balance of Uranus. II. Viscosity of Rock-Ice Mixtures. III. The Thermosphere of Titan", "author": [ { "family_name": "Friedson", "given_name": "Andrew James", "orcid": "0000-0002-7712-0583", "clpid": "Friedson-Andrew-James" } ], "thesis_advisor": [ { "family_name": "Ingersoll", "given_name": "Andrew P.", "orcid": "0000-0002-2035-9198", "clpid": "Ingersoll-A-P" } ], "thesis_committee": [ { "family_name": "Yung", "given_name": "Yuk L.", "orcid": "0000-0002-4263-2562", "clpid": "Yung-Y-L" }, { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" }, { "family_name": "Ingersoll", "given_name": "Andrew P.", "orcid": "0000-0002-2035-9198", "clpid": "Ingersoll-A-P" }, { "family_name": "Muhleman", "given_name": "Duane Owen", "clpid": "Muhleman-D-O" }, { "family_name": "Stevenson", "given_name": "David John", "orcid": "0000-0001-9432-7159", "clpid": "Stevenson-D-J" } ], "local_group": [ { "literal": "Astronomy Department" }, { "literal": "div_gps" } ], "abstract": "Part I:
\r\n\r\nThe seasonal meridional energy balance and thermal structure of the atmosphere of Uranus is investigated using a two-dimensional radiative-convective-dynamical model. Diurnal-average temperatures and heat fluxes are calculated as a function of pressure, latitude, and season. In addition to treating radiation and small-scale convection in a manner typical of conventional radiative-convective models, the dynamical heat fluxes due to large-scale baroclinic eddies are included and parameterized using a mixing length formulation (Stone, 1972; Ingersoll and Porco, 1978). The atmosphere is assumed to be bounded below by an adiabatic, fluid interior with a single value of potential temperature at all latitudes. The internal heat flux is found to vary with latitude and season. The total internal power and the global enthalpy storage rate are seen to oscillate in phase with a period of 1/2 Uranian year. On an annual-average basis, equatorward heat transport can take place in both the atmosphere and the convective interior. For a weak internal heat source, the meridional transport takes place predominantly in the atmosphere. If the internal heat source is larger, a greater share of the transport is taken up by the interior. For a value of the internal heat near the current upper limit for Uranus (~27% of the absorbed sunlight), about 1/3 of the equatorward heat transport at mid-latitudes occurs in the interior. For a given internal heat source, placing the peak of the solar heating at high altitudes or depositing the solar energy into a narrow altitude range favors heat transport by the atmosphere over the interior. Deep penetration of sunlight favors transport by the interior. For the time corresponding to the Voyager 2 Uranus encounter, the effective temperature at the south (sunlit) pole is calculated to be ~1.5 K higher than that at the equator. Horizontal contrasts of the mean 450-900 mbar temperature are found to be less than \u2264 1.5 K, in fair agreement with Voyager 2 IRIS results (Hanel et al., 1986), but the model fails to reproduce the local minimum in this temperature seen at 30\u00b0S. Nevertheless, it is concl uded that meridional heat transport in the atmosphere is efficient in keeping seasonal horizontal temperature contrasts below those predicted by radiative-convective models (Wallace, 1983).
\r\n\r\nPart II:
\r\n\r\nTheory and experiments are used to establish lower and upper bounds on the ratio of actual viscosity to pure ice viscosity for a suspension of rock particles in a water ice matrix. For typical conditions encountered in icy satellites, this ratio is of order ten or possibly larger, depending on unknown factors such as the particle size distribution. It is shown that even this modest increase in viscosity may be enough to have caused a failure of solidstate convective self-regulation early in the evolution of a homogeneous, rock-water ice satellite, provided the satellite is large enough and sufficiently silicate-rich. The criteria for this failure are satisfied by Ganymede and are marginal for Callisto, if the silicates are hydrated. Failure of self-regulation means that the viscosity is too high for the interior to remain completely solid and eliminate the heat production of long-lived radioisotopes by solid state convection. Partial melting of the ice then occurs. It is further shown that satellites of this size may then undergo runaway differentiation into a rock core and almost pure ice mantle, because the gravitational energy release is sufficient to melt nearly all the ice, and the Rayleigh-Taylor instability time scale is short. (Although the high pressure phases of ice melt, the resulting water quickly refreezes at a higher level.) We conjecture that these results explain the striking surface dissimilarity of Ganymede and Callisto, if these satellites accreted cold and undifferentiated. Ganymede may have gone supercritical (melted and differentiated) because of a failure of self-regulation, whereas Callisto remained undifferentiated to the present day. Like all proposed explanations for the Ganymede-Callisto dichotomy, this conjecture cannot be quantified with confidence, because of inadequate or incomplete observations, theory and experimental data.
\r\n\r\nPart III:
\r\n\r\nThe diurnal variation of the vertical structure of Titan's thermosphere is calculated through simultaneous solution of the equations of heat transfer and hydrostatic equilibrium. The temperature and density profiles are found above the mesopause. The dynamical response of the thermosphere to heating is for the most part neglected. Nevertheless, we are able to draw some interesting qualitative and quantitative conclusions regarding the vertical structure. Heating of the upper thermosphere occurs primarily through absorption of solar Lyman \u03b1 radiation by methane, with an additional amount of heating (\u2264 20%) due to low-energy magnetospheric electron precipitation. The heat is conducted downward to the mesopause, where it is removed by IR cooling due principally to acetylene. The mesopause is found to occur where the density is 2.2 x 1012 cm-3 (736 km) and has a temperature of ~110 K. The exospheric temperature is unlikely to exceed 225 K in the course of a Titan day. The diurnally averaged exospheric temperature is in the range 187-197 K, depending on the amount of magnetospheric electron heating that is included in the model. The amplitude of the diurnal variation is found to be \u2264 28 K. We find that the vertical extent of the hydrogen cloud is too large to be explained in terms of simple thermal escape of hydrogen from a ~225 K exosphere and conclude that other processes must be important for populating or heating the neutral torus.
", "doi": "10.7907/65ch-hj35", "publication_date": "1987", "thesis_type": "phd", "thesis_year": "1987" }, { "id": "thesis:7455", "collection": "thesis", "collection_id": "7455", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:01302013-101810609", "primary_object_url": { "basename": "Wenkert_d_1986.pdf", "content": "final", "filesize": 28024085, "license": "other", "mime_type": "application/pdf", "url": "/7455/1/Wenkert_d_1986.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Empirical Relations Between the Earth's Radiation Budget, Cloudiness, and Various Meteorological Parameters", "author": [ { "family_name": "Wenkert", "given_name": "Daniel", "orcid": "0009-0000-4203-7141", "clpid": "Wenkert-Daniel" } ], "thesis_advisor": [ { "family_name": "Ingersoll", "given_name": "Andrew P.", "orcid": "0000-0002-2035-9198", "clpid": "Ingersoll-A-P" } ], "thesis_committee": [ { "family_name": "Muhleman", "given_name": "Duane Owen", "clpid": "Muhleman-D-O" }, { "family_name": "Ingersoll", "given_name": "Andrew P.", "orcid": "0000-0002-2035-9198", "clpid": "Ingersoll-A-P" }, { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" }, { "family_name": "Epstein", "given_name": "Samuel", "clpid": "Epstein-S" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "I have investigated the effect of variation of meteorological variables, cloudiness, and surface variables (such as albedo and continentality) on the reflected solar and emitted terrestrial radiation leaving the top of the atmosphere. The investigation was empirical and used the radiometric data from the scanner channels of the Earth Radiation Budget (ERB) instrument on Nimbus 7, cloudiness variables from analyses done by L. Stowe et al. on data from the Temperature and Humidity Infrared Radiometer (THIR) on Nimbus 7, and meteorological data from the FGGE (First GARP Global Experiment) Level III-b global weather analyses. The data were analysed on time scales of one day and spatial scales of about 450 km.
\r\n\r\nThis investigation had three main goals. The first goal was to determine the effect of cloudiness on the net radiation for various surface and atmospheric conditions during the period investigated (12 June to 18 June 1979). The second goal was to determine whether or not this type of linear analysis on a data set of synoptic time and space scales could be used for a reasonable and empirically accurate parameterization of radiation to be used in simple energy balance climate models (which are valid at vastly larger time and space scales than this data set). The third goal was to compare the regressions determined from this data set between radiation, cloudiness, and weather with the internal statistics developed in a Global Circulation Mode l (GCM), with the idea that eventually this type of linear analysis could be used as a constraint on GCMs used by the atmospheric science community.
\r\n", "doi": "10.7907/5TWR-Z031", "publication_date": "1986", "thesis_type": "phd", "thesis_year": "1986" }, { "id": "thesis:5720", "collection": "thesis", "collection_id": "5720", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:04162010-092926816", "primary_object_url": { "basename": "Paige_da_1985.pdf", "content": "final", "filesize": 7612070, "license": "other", "mime_type": "application/pdf", "url": "/5720/1/Paige_da_1985.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "The Annual Heat Balance of the Martian Polar Caps from Viking Observations", "author": [ { "family_name": "Paige", "given_name": "David Abbey, Jr.", "orcid": "0009-0001-6122-9904", "clpid": "Paige-David-Abbey-Jr" } ], "thesis_advisor": [ { "family_name": "Ingersoll", "given_name": "Andrew P.", "orcid": "0000-0002-2035-9198", "clpid": "Ingersoll-A-P" } ], "thesis_committee": [ { "family_name": "Stevenson", "given_name": "David John", "orcid": "0000-0001-9432-7159", "clpid": "Stevenson-D-J" }, { "family_name": "Murray", "given_name": "Bruce C.", "clpid": "Murray-B-C" }, { "family_name": "Morgan", "given_name": "James J.", "clpid": "Morgan-J-J" }, { "family_name": "Muhleman", "given_name": "Duane Owen", "clpid": "Muhleman-D-O" }, { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" }, { "family_name": "Zurek", "given_name": "Richard W.", "clpid": "Zurek-Richard-W" }, { "family_name": "Ingersoll", "given_name": "Andrew P.", "orcid": "0000-0002-2035-9198", "clpid": "Ingersoll-A-P" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "This thesis presents the first measurements of the annual heat budgets of the polar caps of Mars from spacecraft observations. The primary motivation for this work is to understand why seasonal CO2 frost deposits at the north pole of Mars disappear in the summer, whereas seasonal CO2 deposits near the south pole do not. This behavior is not expected to first order because both Martian poles receive the same total amount of sunlight at the top of the atmosphere over the course of a year. Understanding why the Martian north and south polar caps behave in an asymmetric fashion is important because the vapor pressures of permanent polar CO2 deposits determine the planet-wide surface pressures of CO2 gas, which is the dominant constituent of the Martian atmosphere.
\r\n\r\nAnnual radiation budgets for the core regions of the north and south polar caps are determined from solar reflectance and infrared emission observations obtained by the Infrared Thermal Mappers (IRTMs) aboard the two Viking orbiters. The results show that the absence of CO2 frost at the north pole during summer is primarily due to an asymmetry in the rates of CO2 frost sublimation at surface in the north and south during spring. Further analysis traces this difference to seasonal frost reflectivities being approximately 20% lower in the north than in the south during late spring. It is shown that seasonal frost deposits at the poles demonstrate a remarkable tendency to not become darker when contaminated with dust, and to become brighter with increasing rates of solar illumination. Since peak solar illumination rates are presently higher at the south pole than the north pole because of the large eccentricity of Mars' orbit, the tendency for the frost to become brighter with increasing rates of solar illumination explains the asymmetry. The tendency for the frost to not become darker when contaminated by dust explains why the seasonal behavior of the Martian polar caps is highly repeatable from year to year despite interannual variations in the occurrence of Martian global dust storms.
\r\n\r\nIt is suggested that the unexpected properties of Martian seasonal frost deposits revealed by the results of this study are caused by the tendency for dust particles within the frost to absorb solar radiation, sublimate the solid CO2 that supports them and sink into the frost. If the current behavior of Martian CO2 frost is an indicator to past events, then interactions between dust and frost have exerted a powerful stabilizing influence on the Martian climate system.
", "doi": "10.7907/DPB3-P589", "publication_date": "1985", "thesis_type": "phd", "thesis_year": "1985" }, { "id": "thesis:7490", "collection": "thesis", "collection_id": "7490", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:02212013-144447105", "primary_object_url": { "basename": "Lunine_ji_1985.pdf", "content": "final", "filesize": 46141459, "license": "other", "mime_type": "application/pdf", "url": "/7490/1/Lunine_ji_1985.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Volatiles in the Outer Solar System: I. Thermodynamics of Clathrate Hydrates. II. Ethane Ocean on Titan. III. Evolution of Primordial Titan Atmosphere", "author": [ { "family_name": "Lunine", "given_name": "Jonathan Irving", "orcid": "0000-0003-2279-4131", "clpid": "Lunine-Jonathan-Irving" } ], "thesis_advisor": [ { "family_name": "Stevenson", "given_name": "David John", "orcid": "0000-0001-9432-7159", "clpid": "Stevenson-D-J" } ], "thesis_committee": [ { "family_name": "Stevenson", "given_name": "David John", "orcid": "0000-0001-9432-7159", "clpid": "Stevenson-D-J" }, { "family_name": "Yung", "given_name": "Yuk L.", "orcid": "0000-0002-4263-2562", "clpid": "Yung-Y-L" }, { "family_name": "Ingersoll", "given_name": "Andrew P.", "orcid": "0000-0002-2035-9198", "clpid": "Ingersoll-A-P" }, { "family_name": "Kamb", "given_name": "W. Barclay", "clpid": "Kamb-W-B" }, { "family_name": "Muhleman", "given_name": "Duane Owen", "clpid": "Muhleman-D-O" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "Three investigations are conducted into the physical chemistry of volatiles in the outer solar system and the role of volatiles in icy satellite evolution.
\r\n\r\nPart I:
\r\n\r\nThe thermodynamic stability of clathrate hydrate is calculated under a wide range of temperature and pressure conditions applicable to solar system problems, using a statistical mechanical theory developed by Van der Waals and Platteeuw (1959) and existing experimental data on properties of clathrate hydrates and their components. At low pressure, dissociation pressures and partition functions (Langmuir constants) for CO clathrate (hydrate) have been predicted using the properties of clathrate containing, as guests, molecules similar to CO. The comparable or higher propensity of CO to incorporate in clathrate relative to N2 is used to argue for high CO to N2 ratios in primordial Titan if N2 were accreted as clathrate. The relative incorporation of noble gases in clathrate from a solar composition gas at low temperatures is calculated, and applied to the case of giant planet atmospheres and icy satellites. It is argued that non-solar but well-constrained noble gas abundances would be measured by Galileo in the Jovian atmosphere if the observed carbon enhancement were due to bombardment of the atmosphere by clathrate-bearing planetesimals sometime after planetary formation. The noble gas abundances of Titan's atmosphere are also predicted under the hypothesis that much of the satellite's methane accreted as clathrate. Double occupancy of clathrate cages by H2 and CH4 in contact with a solar composition gas is examined, and it is concluded that potentially important amounts of H2 may have incorporated in satellites as clathrate. The kinetics of clathrate formation is also examined, and it is suggested that, under thermodynamically appropriate conditions, essentially complete clathration of water ice could have occurred in high pressure nebulae around giant planets but probably not in the outer solar nebula; comets probably did not aggregate as clathrate. At moderate pressures, the phase diagram for methane clathrate hydrate in the presence of 15% ammonia (relative to water) is constructed, and application to the early Titan atmospheric composition is described. The high pressure stability of CH4, N2, and mixed CH4-N2 clathrate hydrate is calculated; conversion back to water and CH4 and/or N2 fluids or solids is predicted for pressures \u227312 kilobars and/or temperatures \u2273320 K. The effect of ammonia is to shrink the T-P stability field of clathrate with increasing ammonia concentration. A preliminary phase diagram for the high pressure ammonia-water system is constructed using new data of Johnson et al. (1984). These results imply that 1) clathrate is stable throughout the interior of Oberon- and Rhea-sized icy satellites, and 2) clathrate incorporated in the inner-most icy regions of Titan would have decomposed, perhaps allowing buoyant methane to rise. Brief speculation on the implications of this conclusion for the origin of surficial methane on Titan is given. A list of suggested experiments and observations to test the theory and its predictions is presented.
\r\n\r\nPart II:
\r\n\r\nWe propose a global Titanic ocean, one to several kilometers deep, the modern composition of which is predominantly ethane. If the ocean is in thermodynamic equilibrium with an atmosphere of 3' (mole fraction) methane then its composition is roughly 70% C2H6, 25% CH4, and 5% N2. Photochemical models predict that C2H6 is the dominant end-product of CH4 photolysis so that the evolving ocean is both the source and sink for ongoing photolysis. The coexisting atmosphere is compatible with Voyager data. Two consequences are pursued: the interaction of such an ocean with the underlying \"bedrock\" of Titan (assumed to be water-ice or ammonia hydrate) and with the primarily nitrogen atmosphere. It is concluded that although modest exchange of oceanic hydrocarbons with enclathrated methane in the bedrock can in principle occur, it is unlikely for reasonable regolith depths and probably physically inhibited by the presence of a layer of solid acetylene and complex polymeric hydrocarbons a couple of hundred meters thick at the base of the ocean. However, the surprisingly high solubility of water ice in liquid methane (Rebiai et al., 1983) implies that topographic features on Titan of order 100 meter in height can be eroded away on a time scale \u227e109 years; \"Karst\" topography could be formed. Finally, the large solubility difference of N2 in methane versus ethane implies that the ocean composition is a strong determinant of atmospheric pressure; a simple radiative model of the Titan atmosphere is employed to demonstrate that significant surface pressure and temperature changes can occur as the oceanic composition evolves with time. The model suggests that the early methane-rich ocean may have been frozen; scenarios for evolution to the present liquid state are discussed.
\r\n\r\nPart III:
\r\n\r\nA simple convective cooling model of a primordial, CH4-NH3-N2 Titan atmosphere is constructed, in an effort to understand the fate of volatiles accreted from a gaseous disk (\"nebula\") surrounding Saturn and released from accreting planetesimals during the satellite's formation. Near-surface temperatures are initially \u2273400 K consistent with the large amount of energy supplied to the atmosphere during accretion. As a consequence of accretional heating, the upper mantle of the satellite consists of an ammonia-water liquid, extending to the surface. This \"magma ocean\" is the primary buffer of atmospheric cooling because it is \u227310 times as massive as the atmosphere. The radiative properties of the atmosphere are assumed independent of frequency and the resulting temperature profile is found to be adiabatic; if the atmosphere contains dark particulates surface temperatures could be lower than calculated here. Three major processes drive the cooling: (1) hydrodynamic escape of gas from the top of the atmosphere, which determines the cooling time scales, (2) atmospheric ablation by high velocity impacts (not modeled in detail here), and (3) formation of clathrate hydrate at the ocean-atmosphere interface, at T \u2264 250 K. Cooling time scales driven by escape are sufficiently long (108-109 years) to allow ~10 bars of N2 to be produced photochemically from NH3 in the gas phase (Atreya et al., 1978); however, the abundance of NH3 at temperatures \u227e150 K (where the intermediate photochemical products condense out) is optically thick to the dissociative UV photons. Thus, N2 formation may proceed primarily by shock heating of the atmosphere during large body impacts, as well as by photochemistry (1) at T < 150 K if intermediate products supersaturate, or (2) in a warm stratosphere, with NH3 abundance fixed by its tropopause value. The clathrate formed during late stages of cooling sequesters primarily CH4, with some N2, and forces surface temperatures and pressures to drop rapidly. The clathrate is only marginally buoyant relative to the coexisting ammonia-water liquid. If it sinks, the atmosphere is driven to an N2-rich state with most of the methane sequestered in clathrate when the ocean surface freezes over at ~180 K. Implications of this scenario for the present surface state of Titan are contrasted with those obtained if the clathrate forms a buoyant crust at the surface.
", "doi": "10.7907/tw6n-qa60", "publication_date": "1985", "thesis_type": "phd", "thesis_year": "1985" }, { "id": "thesis:7454", "collection": "thesis", "collection_id": "7454", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:01302013-100511748", "primary_object_url": { "basename": "Summers_me_1985.pdf", "content": "final", "filesize": 18944426, "license": "other", "mime_type": "application/pdf", "url": "/7454/1/Summers_me_1985.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Theoretical Studies of Io's Atmosphere", "author": [ { "family_name": "Summers", "given_name": "Michael Earl", "orcid": "0000-0001-5986-8902", "clpid": "Summers-Michael-Earl" } ], "thesis_advisor": [ { "family_name": "Ingersoll", "given_name": "Andrew P.", "orcid": "0000-0002-2035-9198", "clpid": "Ingersoll-A-P" } ], "thesis_committee": [ { "family_name": "Epstein", "given_name": "Samuel", "clpid": "Epstein-S" }, { "family_name": "Muhleman", "given_name": "Duane Owen", "clpid": "Muhleman-D-O" }, { "family_name": "Yung", "given_name": "Yuk L.", "orcid": "0000-0002-4263-2562", "clpid": "Yung-Y-L" }, { "family_name": "Cohen", "given_name": "Judith G.", "orcid": "0000-0002-8039-4673", "clpid": "Cohen-J-G" }, { "family_name": "Ingersoll", "given_name": "Andrew P.", "orcid": "0000-0002-2035-9198", "clpid": "Ingersoll-A-P" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "A range of theoretical models of the compositional structure of Io's dayside atmosphere and ionosphere are developed. The dominant neutral gas, SO2, is provided by sublimation of surface frost. Photochemical processes lead to the build up of O, S, SO, and O2 as minor gasses near Io's surface while O becomes the dominant gas near the exobase. The vertical column density of O2 in all models considered is less than 1014 cm-2. The dayside ionosphere is formed as a result of ionization of neutral species by solar UV radiation. Charge exchange and rearrangement reactions are important for determining the ionic composition of the ionosphere. The dominant ion in the models considered is SO+. A number of charge exchange reactions are identified whose rates need to be better determined in order to refine the present model of the ionosphere. The best matches of the model ionospheres to that observed by the Pioneer 10 radio occultation experiment require atmospheric surface concentrations of SO2 in the range of 2.5 x 109 to 1 x 1011 cm-3, and an exospheric temperature in the range of 960 K to 1230 K. The ratio of the escape fluxes of O to S from the exobase is \u2265 2 in the models considered, while the models which allow surface deposition of minor constituents always have a total sulfur depositional rate greater than 1/2 of the total oxygen depositional rate, thus a surface enrichment of S relative to that predicted by a pure SO2 surface. The depositional rate of this \"excess\" sulfur is in the range 100 m to 1 km thickness per billion years.
\r\n\r\nAtmospheric Na is provided by surface sputtering of SO2 surface frost with Na impurities by MeV type magnetospheric ions. An upward flux of Na2O of S x 107 cm-2 s-1 leads to an escape flux of Na from the exobase of 1 x 107 cm-2 s-1. The chemistry (ion and neutral) of Na species in the atmosphere has only minor effects on the major characteristics of the atmosphere and ionosphere.
\r\n\r\nIt is generally accepted that Io is the source of S, O, Na, and K which, subsequent to ionization, form the constituents of the Io plasma torus. It is shown in chapter II that the escape of S and O from Io can be understood in terms of the photochemistry of a predominantly SO2 atmosphere created by the high vapor pressure of SO2. However, the vapor pressures of Na2S, K2S and other common compounds containing Na and K are negligible at the surface temperature of Io. In chapter III we propose that Na and K escape from Io in two stages. Atoms of Na and K (or molecules containing these atoms) are first sputtered into the atmosphere from the surface by high energy magnetospheric ions. Atmospheric sputtering by low energy corotating ions then removes these constituents (along with others present) out of Io's gravitational control. The estimated injection rates are sufficiently large to maintain the observed Na, K, and O clouds observed around Io.
", "doi": "10.7907/rsm8-qh33", "publication_date": "1985", "thesis_type": "phd", "thesis_year": "1985" }, { "id": "thesis:11210", "collection": "thesis", "collection_id": "11210", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:10012018-103419193", "type": "thesis", "title": "Photochemical Modeling of the Earth's Stratosphere", "author": [ { "family_name": "Froidevaux", "given_name": "Lucien", "orcid": "0000-0002-0681-1483", "clpid": "Froidevaux-Lucien" } ], "thesis_advisor": [ { "family_name": "Muhleman", "given_name": "Duane Owen", "clpid": "Muhleman-D-O" } ], "thesis_committee": [ { "family_name": "Muhleman", "given_name": "Duane Owen", "clpid": "Muhleman-D-O" }, { "family_name": "DeMore", "given_name": "William B.", "clpid": "DeMore-William-B" }, { "family_name": "Epstein", "given_name": "Samuel", "clpid": "Epstein-S" }, { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" }, { "family_name": "Yung", "given_name": "Yuk L.", "orcid": "0000-0002-4263-2562", "clpid": "Yung-Y-L" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "We have helped develop a one-dimensional photochemical model of the Earth's stratosphere, in order to provide an up-to-date comparison with mid-latitude observations. This work focuses on the present state of the stratosphere, and includes studies of the radiation field (absorption and scattering), the important partitioning and vertical distribution of halo-carbons and their products, as well as certain intriguing discrepancies related to light and heavy ozone.
\r\n\r\nWe briefly comment on the detection by J. R. Herman and J. E. Mentall of a 10% ratio of total scattered flux to direct solar flux at a wavelength of about 200 nm and an altitude of 40 km. This ratio is over a factor of two higher than our theoretical results and cannot be explained without the existence of a scattering component not included in the model. We also explicitly demonstrate the first-order effects of the inclusion of sphericity (spherical shell atmosphere) on the stratospheric photochemistry at solar zenith angles close to 90\u00b0. The resulting changes in model concentrations for short-lived radicals such as O, OH, ClO, and NO are largest in the lower stratosphere, but relatively small compared to current observational uncertainties.
\r\n\r\nWe propose that a significant overestimate of the molecular oxygen absorption cross sections in the important spectral window from about 200 to 220 nm is in large part responsible for the discrepancy between observed and modeled vertical profiles of some halocarbons (CFCl3 in particular), as well as for the long-standing problem of simultaneously fitting N2O, CH4, CF2Cl2, and CFCl3 profiles with a single eddy diffusion model. Recent measurements of atmospheric transmission by J. R. Herman and coworkers seem to support this idea. The use of their proposed reduction in O2 cross sections leads to significant decreases in the CFCl3 concentration above about 20 km, with smaller reductions in N2O, CF2Cl2 and HNO3. The concentrations of CH4, H2, and CO are not significantly altered. Changes in other gases (including ozone) are also discussed, as well as the effect on eddy diffusion coefficients obtained from measurements of N2O or CH4 profiles in the stratosphere. Accurate determinations of these small O2 absorption cross sections are needed, since they affect the vertical distribution of halo-carbons in the stratosphere, and the lifetime of these species has an impact on ozone depletion estimates.
\r\n\r\nIn terms of the halocarbon decomposition products in the stratosphere, our model vertical distribution of ClO is shown to provide a reasonably good fit to the mean of available observations. As discussed by others, changes in certain rate constants affecting HOx in the lower stratosphere have led to decreases in model ClO concentrations by over a factor of three in the lower stratosphere, thus improving the shape of the vertical profile. In addition, the amount of upper stratospheric ClO has increased due to recent changes in the kinetics (reactions O + HO2, O + ClO, and possibly OH + HCl). The diurnal variation of ClO observed from the ground (microwave emission) by P. Solomon and coworkers is consistent with our model results in terms of the maximum day-to-night decrease in column abundance above about 30 km. However, the observed mid-morning increase is slower than theoretical values, while the predicted afternoon decrease might be too slow, even if one considers the uncertainties in photochemical data. This could indicate the existence of missing chemistry in the models. Although the different observations show somewhat contradictory results. Other observations (balloon-borne microwave spectroscopy and infrared laser radiometry) are also discussed in relation to our model. To first-order, indirect evidence for the breathing cycle between ClO and ClONO2 seems to have been established. The mean observed HCl mixing ratio profile decreases somewhat faster towards the lower stratosphere than model profiles, a discrepancy which has previously been noted, particularly at high latitudes. Measurements of ethane in the lower stratosphere seemed to indicate that the atomic chlorine concentration was three to five times lower than predicted, but more recent data do not show such a discrepancy.
\r\n\r\nThe fluorine products consist mostly of HF and COF2. We show that the main uncertainty for this system is the value of the quantum yield (as a function of wavelength) for COF2 photodissociation, which translates into a factor of three or more uncertainty in the ratio of HF to COF2 concentrations in the upper stratosphere. If this quantum yield has an average value close to 0.25, a better model fit to observations of HF and [HF]/[HCl] is obtained than if the value is close to unity. Simultaneous stratospheric measurements of COF2 and HF, as well as ClO and HCl, would greatly enhance our ability to test photochemical models of these halocarbon products.
\r\n\r\nFinally, we stress that, although generally good agreement is found between our model and observations of HOx, NOx, and ClOx species (involved in catalytic cycles destroying ozone), the mean observed mid-latitude ozone abundance from about 35 to 50 km is up to 50 or 60% greater than current model results. Certain observations of a 10 to 15% daytime increase in ozone concentration in the 30 to 40 km region are also puzzling, if real. We explore the model sensitivity to various input parameters and point out that, given the present uncertainties in photochemical laboratory data, no reasonable change in one or even three or four of these parameters can eliminate the ozone discrepancy. There might well be some missing chemistry in relation to the effectiveness of the loss processes for odd oxygen, or a (less likely) unknown significant O3 source. We have to understand the present upper stratospheric ozone distribution, before estimates of possible future ozone depletion can be made with confidence. We also discuss our understanding of heavy ozone photochemistry, which might be related to a light ozone photochemical source. Fast isotopic exchange processes between O and O2 will dominate the heavy odd oxygen chemistry, and we do not find any significant heavy ozone enhancement possibilities in the stratosphere, unless unusually large fractionation processes exist. The in situ mass spectrometer observations of a 40% enhancement in 18O32O2 near 30 km by K. Mauersberger remain a mystery, and further data collection -- possibly via infrared or microwave spectroscopy as well -- should be undertaken if this potentially significant discrepancy is to be understood.
", "doi": "10.7907/hzdt-5z21", "publication_date": "1984", "thesis_type": "phd", "thesis_year": "1984" }, { "id": "thesis:3677", "collection": "thesis", "collection_id": "3677", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-09212004-110904", "primary_object_url": { "basename": "Porco_cc_1983.pdf", "content": "final", "filesize": 5964354, "license": "other", "mime_type": "application/pdf", "url": "/3677/1/Porco_cc_1983.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Voyager Observations of Saturn's Rings. 1. The Eccentric Rings at 1.29, 1.45, 1.95 and 2.27 R\u209b. 2. The Periodic Variation of Spokes", "author": [ { "family_name": "Porco", "given_name": "Carolyn C.", "clpid": "Porco-Carolyn-C" } ], "thesis_advisor": [ { "family_name": "Muhleman", "given_name": "Duane Owen", "clpid": "Muhleman-D-O" } ], "thesis_committee": [ { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" }, { "family_name": "Stevenson", "given_name": "David John", "orcid": "0000-0001-9432-7159", "clpid": "Stevenson-D-J" }, { "family_name": "Sargent", "given_name": "Wallace L. W.", "clpid": "Sargent-W-L-W" }, { "family_name": "Muhleman", "given_name": "Duane Owen", "clpid": "Muhleman-D-O" }, { "family_name": "Ingersoll", "given_name": "Andrew P.", "orcid": "0000-0002-2035-9198", "clpid": "Ingersoll-A-P" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "Part 1:
\r\n\r\nFive major eccentric features in the rings of Saturn are studied. These are the outer A and B ring edges at 1.95 and 2.27 R\u209b and three narrow ringlets at 1.29, 1.45, and 1.95 R\u209b. Data acquired by four Voyager experiments - Imaging Science (ISS), Radio Science (RSS), Ultraviolet Spectrometer (UVS), and Photopolarimeter(PPS) - were used in this investigation.
\r\n\r\nThe shapes and kinematics of the A and B ring outer edges are determined by their proximity to strong low-order Lindblad resonances. The data for the A ring edge are consistent with a 7-lobed distortion rotating with the mass-weighted mean angular velocity of the co-orbital satellite system. The B ring edge has a double-lobed figure which rotates with the mean motion of Mimas.
\r\n\r\nThe Saturnian ringlets are narrow (mean widths vary from ~ 10-60 km) and have eccentricities of order 10-4. All have sharp edges, normal optical depths \u03c4 ~ 1-2, and are embedded in essentially empty gaps (\u03c4 < 0.05). The Titan ring at 1.29 R\u209b and the Huygens ring at 1.45 R\u209b exhibit positive linear width-radius relations; the Maxwell ring at 1.95 R\u209b does not. The kinematics of the Huygens ring are determined solely by Saturn's non-spherical gravity field. The kinematics of the Titan ring are apparently completely determined by its interaction with Titan. At present, the most plausible model for the Maxwell ring involves the superposition of two components: one which is freely precessing and the other which is forced by Mimas and the elliptical B ring. Masses, mean surface mass densities, and specific opacities have been calculated for the Titan and Huygens rings.
\r\n\r\nPart 2:
\r\n\r\nThe discovery of a periodic variation in spoke activity in Saturn's rings from the analysis of Voyager images is reported. A Fourier power spectrum was computed using a data set generated by quantifying spoke activity observed on the morning (western) half of the rings in Voyager images spanning ~ 12 Saturn rotations and in Voyager 2 images spanning ~ 90 Saturn rotations. The period from Voyager 1 data is 631 \u00b1 22 min; from Voyager 2, 640.6 \u00b1 3.5 min. The latter result suggests that the fundamental modulation in spoke activity is due to the rotation of Saturn's magnetic field, the period of which is 639.4 min. Maximum spoke activity observed anywhere on the rings is most likely to be associated with the region of the magnetic field responsible for the most intense emission of the Saturn Kilometric Radiation (SKR). Passage of this region through Saturn's shadow may play a significant role in the creation and/or rejuvenation of spokes.
\r\n", "doi": "10.7907/q3z6-ca90", "publication_date": "1983", "thesis_type": "phd", "thesis_year": "1983" }, { "id": "thesis:11778", "collection": "thesis", "collection_id": "11778", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:08302019-112320091", "primary_object_url": { "basename": "Chael_EP_1983.pdf", "content": "final", "filesize": 32931097, "license": "other", "mime_type": "application/pdf", "url": "/11778/1/Chael_EP_1983.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Constraints on the Earth's Anelastic and Aspherical Structure from Antipodal Surface Waves", "author": [ { "family_name": "Chael", "given_name": "Eric Paul", "clpid": "Chael-Eric-Paul" } ], "thesis_advisor": [ { "family_name": "Helmberger", "given_name": "Donald V.", "clpid": "Helmberger-D-V" } ], "thesis_committee": [ { "family_name": "Anderson", "given_name": "Donald L.", "clpid": "Anderson-D-L" }, { "family_name": "Kanamori", "given_name": "Hiroo", "orcid": "0000-0001-8219-9428", "clpid": "Kanamori-H" }, { "family_name": "Harkrider", "given_name": "David G.", "clpid": "Harkrider-D-G" }, { "family_name": "Muhleman", "given_name": "Duane Owen", "clpid": "Muhleman-D-O" }, { "family_name": "Clayton", "given_name": "Robert W.", "orcid": "0000-0003-3323-3508", "clpid": "Clayton-R-W" }, { "family_name": "Helmberger", "given_name": "Donald V.", "clpid": "Helmberger-D-V" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "Seismograms recorded at antipodal distances (\u0394~180\u00b0) are used to measure the attenuation and dispersion of surface waves. The antipode is a focus for surf ace wave energy radiated at all directions from the source. Antipodal records thus give direct estimates of global average properties. Laterally heterogeneous Earth structure degrades the focusing and complicates the data analysis.
\r\n\r\nGroup velocity and Q of 120-300 s Rayleigh waves are obtained from a record (station PTO) of the May 23, 1968 New Zealand earthquake. The effects of aspherical structure on this record are simulated by generating synthetic seismograms for an ellipsoidal Earth. The results show that the bias in antipodal Q measurements varies with time. This property is used to constrain the bias in the PTO measurements.
\r\n\r\nA seismogram of the August 19, 1977 Indonesian earthquake from station TRN is used to study 250-500 s Rayleigh waves. This record is synthesized by combining first order perturbation theory with a realistic representation of the Earth's heterogeneities. Analysis of the synthetic shows that Q measured from the TRN record is biased as much as 20% and that group velocities are virtually unbiased. The PTO and TRN data yield global average values of Rayleigh wave Q which are comparable to or slightly below those for the model PREM [Dziewonski and Anderson, 1981].
\r\n\r\nAntipodal Love wave and spheroidal overtone data are also presented. Synthetic seismograms match the observed arrivals well, demonstrating that these wave modes can be profitably studied at the antipode.
", "doi": "10.7907/xe9f-zz51", "publication_date": "1983", "thesis_type": "phd", "thesis_year": "1983" }, { "id": "thesis:7461", "collection": "thesis", "collection_id": "7461", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:02042013-113709002", "primary_object_url": { "basename": "Gladstone-gr-1983.pdf", "content": "final", "filesize": 23291604, "license": "other", "mime_type": "application/pdf", "url": "/7461/1/Gladstone-gr-1983.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Radiative Transfer and Photochemistry in the Upper Atmosphere of Jupiter", "author": [ { "family_name": "Gladstone", "given_name": "George Randall", "clpid": "Gladstone-George-Randall" } ], "thesis_advisor": [ { "family_name": "Muhleman", "given_name": "Duane Owen", "clpid": "Muhleman-D-O" } ], "thesis_committee": [ { "family_name": "Muhleman", "given_name": "Duane Owen", "clpid": "Muhleman-D-O" }, { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" }, { "family_name": "Yung", "given_name": "Yuk L.", "orcid": "0000-0002-4263-2562", "clpid": "Yung-Y-L" }, { "family_name": "Ingersoll", "given_name": "Andrew P.", "orcid": "0000-0002-2035-9198", "clpid": "Ingersoll-A-P" }, { "family_name": "Burnett", "given_name": "Donald S.", "orcid": "0000-0001-9521-8675", "clpid": "Burnett-D-S" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "The upper atmosphere of Jupiter, from the tropopause to well above the homopause, is investigated as to its compositional structure and vertical mixing parameters. Constraints are obtained through the study of the radiative transfer of ultraviolet resonance lines and continuum radiation. These constraints and others are then used in the modeling of the hydrocarbon photochemistry of Jupiter.
\r\n\r\nA direct finite difference numerical solution for the equation of radiative transfer is developed for use in planetary atmospheres. The procedure uses a plane-parallel atmosphere, and can treat partial frequency redistribution (for use in the radiative transfer of optically thick resonance lines), inhomogeneity, external or internal sources, and various boundary conditions. Isotropic scattering is assumed, but in the case of no frequency redistribution, a Rayleigh phase function may be used. A program utilizing this solution is tested against more powerful and elaborate methods. This program is then applied to the Lyman-\u03b1 aurora of Jupiter, and detailed line profiles are presented.
\r\n\r\nUsing this program, a study is made of the UV reflection spectrum of Jupiter as measured by the International Ultraviolet Explorer. Detailed modeling reveals the mixing ratios of C2H2, C2H6, and C4H2 to be (1.0 \u00b1 0.1) x 10-7, (6.6 \u00b1 5.3) x 10-6, and (2.9 \u00b1 2.0) x 10-10, respectively in the pressure region between \u223c 3 and 40 mbar. Upper limits in this pressure region for the mixing ratios of C2H4 and NH3 were determined to be (3.9 \u00b1 4.93.9) x 10-10 and (4.2 \u00b1 6.74.2 x 10-9, respectively. An upper limit to the optical depth of dust above the tropopause, assuming it is well mixed, is 0.2 \u00b1 0.30.2 and an upper limit on the dayglow emission by the Lyman bands of H2 is 1.4 \u00b1 2.41.4 kiloRayleighs. Comparison with Voyager results suggests that the scale height of C2H2 in the region 150-10 mbar is approximately twice that of the bulk atmosphere, consistent with the IUE observation of cosine-like limb darkening in the north-south direction on Jupiter in the UV.
\r\n\r\nThe resonant scattering of the solar He I 584 \u00c5 emission line by the upper Jovian atmosphere is investigated next. The observed intensity of this scattered line depends directly on the eddy diffusion for vertical mixing (Kh) and the temperature (Th) at the homopause. Using the temperature profile determined by the Voyager UVS experiment, a value of Kh = 1.3 x 106 cm2s-1 \u00b1 30% is obtained. If the temperature profile was the same during the Pioneer 10 encounter with Jupiter, then Kh \u2248 1 x 108 cm2 s-1 at that time. The He 584 \u00c5 brightness is found not to depend strongly on the gradients of either the eddy diffusion or temperature profiles. A semi-analytical expression for computing the He 584 \u00c5 brightness for a constant-K, constant-T atmosphere is derived and compared with calculations by other authors. It is speculated that the apparent decrease in Kh by two orders of magnitude between the Pioneer and Voyager encounters may be the result of an increase in the pole-to-equator circulation in the thermosphere, perhaps driven by the solar cycle.
\r\n\r\nThe above results are used as constraints for a one-dimensional photochemical-diffusive model of the hydrocarbon chemistry in Jupiter's upper atmosphere. The important chemical cycles and pathways among the C and C2 species are outlined and it is shown that the amount of methane dissociation resulting from acetylene photochemistry is comparable to the amount that is due to direct photolysis. Profiles for the major observed hydrocarbon species are calculated and their sensitivity to eddy diffusion profile, chemistry, and solar UV flux is examined. A best fit to the eddy diffusion profile of the upper atmosphere during the Voyager encounters is found to be given by K = 1.3 x 106(2.17 x 1013/n)0.5 cm2 s-1 (where n is the total number density), which implies a vertical mixing time at the tropopause of ~ 50 years. It is shown that polyacetylene formation driven by acetylene photochemistry in the models presented here is capable of producing the observed abundance of Danielson dust in the stratosphere of Jupiter. The disk-averaged Lyman-\u03b1 albedo of the the preferred model is calculated to be ~ 8 kiloRayleighs, almost a factor of two lower than the Voyager observed value of ~ 14 kiloRayleighs. This may indicate the need for an increased flux of atomic hydrogen from the thermosphere over the already present source from EUV and soft electron dissociation of H2. Such a flux is available from the auroral regions if there exists a pole-to-equator flow in the thermosphere as postulated earlier. Finally, a brief consideration of the auroral chemistry concludes that more lab studies of ion-neutral and ion-electron recombination reactions are needed before a meaningful study of that problem may be undertaken.
", "doi": "10.7907/pzzp-2209", "publication_date": "1983", "thesis_type": "phd", "thesis_year": "1983" }, { "id": "thesis:7441", "collection": "thesis", "collection_id": "7441", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:01252013-152959933", "type": "thesis", "title": "Carbon Monoxide in the Atmospheres of the Terrestrial Planets", "author": [ { "family_name": "Clancy", "given_name": "Robert Todd", "clpid": "Clancy-Robert-Todd" } ], "thesis_advisor": [ { "family_name": "Muhleman", "given_name": "Duane Owen", "clpid": "Muhleman-D-O" } ], "thesis_committee": [ { "family_name": "Ingersoll", "given_name": "Andrew P.", "orcid": "0000-0002-2035-9198", "clpid": "Ingersoll-A-P" }, { "family_name": "Burnett", "given_name": "Donald S.", "orcid": "0000-0001-9521-8675", "clpid": "Burnett-D-S" }, { "family_name": "Moffet", "given_name": "Alan Theodore", "clpid": "Moffet-A-T" }, { "family_name": "Muhleman", "given_name": "Duane Owen", "clpid": "Muhleman-D-O" }, { "family_name": "Yung", "given_name": "Yuk L.", "orcid": "0000-0002-4263-2562", "clpid": "Yung-Y-L" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "Microwave spectra of carbon monoxide (12CO) in the mesosphere of Venus were measured in December of 1978; May and December of 1980; and January, September, and November of 1982. These spectra are analyzed to provide mixing profiles of CO in the Venus mesosphere and best constrain the mixing profile of CO between ~ 100 and 80 kilometers altitude. From the January 1982 measurement (which, of all our spectra, best constrains the abundance of CO below 80 km altitude) we find an upper limit for the CO mixing ratio below 80 kilometers altitude that is 2-3 times smaller than the stratospheric ( ~ 65 km) value of 4.5 \u00b1 1.0 x 10-5 determined by Connes et al. (1968) in 1967, indicating a possible long-term change in the lower atmospheric concentration of CO.
\r\n\r\nIntercomparison among the individual CO profiles derived from our spectra indicates considerable short-term temporal and/or spatial variation in the profile of CO mixing in the Venus mesosphere above 80 kilometers. A more complete comparison with previously published CO microwave spectra from a number of authors (Kakar et al., 1976; Gulkis et al., 1977: Schloerb et al., 1980; Wilson and Klein, 1981; Schloerb et al., 1981) specifies the basic diurnal nature of mesospheric CO variability. CO abundance above ~ 95 kilometers in the Venus atmosphere shows approximately a factor of 2-4 enhancement on the nightside relative to the dayside of Venus. The magnitude of this nightside CO bulge is in good agreement with the dynamical modeling results of Dickinson and Ridley (1977), indicating that subsolar to antisolar circulation proposed for the thermosphere of Venus by Dickinson and Ridley extends to below 100 km altitude in the Venus mesosphere. Furthermore, peak nightside CO abundance above ~ 95 kilometers occurs very near to the antisolar point on Venus (local time of peak CO abundance above ~ 95 kilometers occurs at 0.6+0.7-0.6 hours after midnight on Venus), strongly suggesting that retrograde zonal flow is substantially reduced at an altitude of 100 kilometers in the Venus mesosphere.
\r\n\r\nBy contrast, CO abundances between 80 and 90 kilometers altitude show a maximum that is shifted from the antisolar point towards the morning side of Venus (local time of peak CO abundance between 80 and 90 kilometers occurs at 8.5 \u00b1 1.0 hours past midnight on Venus). The magnitude of the diurnal variation of CO abundance between 80 and 90 kilometers is again, approximately a factor of 2-4. Given the recombination of CO strongly peaks in this altitude region (Yung and DeMore, 1982), we investigated the possible effects of diurnal photochemistry as a driving force for diurnal CO variations between 70 and 90 kilometers from model calculations. We find that the likely magnitude of diurnal CO variability due to photochemistry and vertical eddy diffusion is smaller than that indicated by the microwave data, and that such variations cannot predict the observed phase behavior of the diurnal variations. Photochemical models invariably predict peak CO abundances in the afternoon rather than morning hours on Venus. However, a simple model for the circulation of the Venus mesosphere is presented to explain the observed diurnal variations of CO both above 90 kilometers altitude and between 80 and 90 kilometers altitude. We propose that the subsolar to antisolar circulation of the Venus thermosphere (and the resulting nightside enhancement of CO) persists down to altitudes of ~ 80 kilometers. Above ~ 90 kilometers zonal flow is small and the nightside CO bulge remains centered near the antisolar point on Venus. Below ~ 90 kilometers altitude retrograde zonal wind velocities increase abruptly to several tens of meters/sec displacing the nightside enhancement of CO towards the morningside of Venus.
\r\n\r\nWe also present a J = 1 \u2192 2 spectrum of 13CO absorption in the mesosphere of Venus. This 13CO spectrum was measured at the same time as our high quality, January 1982 12CO spectrum. Radiative transfer models employing a single pressure-temperature model of the Venus mesosphere are fit to both the 13CO and 12CO spectra. The 12CO spectrum is used to specify the altitude distribution of CO. Subsequently, we solve for the ratio 12CO/13CO = 185 in order to best fit the 13CO spectrum. Based on an extensive error analysis we believe that the standard deviation of this value is \u00b1 69. This result applies only to the mesosphere of Venus, i.e. from 80 to 110 km. Values of the 12CO/13CO ratio measured deeper in the Venus atmosphere are closer to the terrestrial value of 89. We suggest several fractionation mechanisms in order to account for the difference between our result and the terrestrial value. However, as yet, none of these mechanisms is known to produce significant fractionation of CO isotopes in the upper atmosphere of Venus.
\r\n\r\nIn January of 1982 we measured a microwave spectrum of CO in the Martian atmosphere utilizing the rotational J = 1 \u2192 2 transition of CO. We have analyzed our data and reanalyzed the microwave spectra of Kakar et al. (1967, measured in 1975) and Good and Schloerb (1981, measured in 1980) in order to constrain estimates of the temporal variability of CO abundance in the Martian atmosphere. Long-term (\u2273 1 year) variations in CO abundance have been predicted on the basis of possible variations in eddy diffusion (McElroy and Donahue, 1972) and/or condensible HxOy compounds (Hunten, 1974) in the Martian atmosphere. Our values of CO column density from the data of Kakar et al., Good and Schloerb, and our own are 1.7 \u00b1 0.9 x 1020 cm-2, 3.0 \u00b1 1.0 x 1020 cm-2, and 4.6 \u00b1 2.0 x 1020 cm-2, respectively. The most recent estimate of CO column density from the 1967 infrared spectra of Connes et al. (1969) is 2.0 \u00b1 0.8 x 1020 cm-2 (Young and Young, 1977). The large uncertainties given for the microwave measurements are due primarily to uncertainty in the difference between the continuum brightness temperature and atmospheric temperatures of Mars. We have accurately calculated the variation among the observations of the continuum (surface) brightness temperature of Mars which is primarily a function of the observed aspect of Mars. A more difficult problem to consider is variability of global atmospheric temperatures among the observations, particularly the effects of global dust storms and the ellipticity of the orbit of Mars. The large error bars accompanying our estimates of CO column density from the three sets of microwave measurements are primarily caused by an assumed uncertainty of \u00b1 10 K in our atmospheric temperature model due to possible dust in the atmosphere. A qualitative consideration of seasonal variability of global atmospheric temperatures among the measurements suggests that there is not strong evidence for variability of the column abundance of CO on Mars, although variability of 0-100% over a time scale of several years is allowed by the data set. The implication for the variability of Mars O2 (which is directly tied to photodissociation of CO2) is, crudely, a factor of two less. We find that the altitude distribution of C) in the atmosphere of Mars is not well constrained by any of the spectra, although our spectrum is marginally better fit by an altitude increasing profile of CO mixing ratios.
\r\n\r\nFinally, we consider variations in the CO content of the terrestrial mesosphere. The Earth's mesospheric carbon monoxide was observed in absorption against the Moon in early December of 1979 and late January of 1982 at a wavelength of 1.3 mm, and in early December of 1980 at a wavelength of 2.6 mm. The January 1982 spectrum was also measured in emission with very high signal-to-noise ratios. The observed wavelengths correspond to the respective rotational transitions of CO, J = 1 \u2192 2 and J = 0 \u2192 1. No significant change in the column density of CO above ~ 65 km is found between the 1979 and 1980 observations, but the January 1982 measurement indicates an ~ 30% reduction in column density relative to the December observations. Inversion of the spectra did not provide unique CO mixing ratio profiles for a direct quantitative comparison of December 1979 and 1980 and January 1982 profiles, due to limited signal-to-noise ratios for the 1979, 1980 observations. One of the best constrained mixing profiles published to date is presented for the very high signal-to-noise January 1982 emission spectrum. Comparison with other published spectra of mesospheric CO suggests a large seasonal variation (~ a factor of 2-4) in the column density of CO above 65 km, with a maximum in winter and a minimum in summer. The phase of this seasonal variation in CO abundance is opposite to the phase of seasonal variation in insolation suggesting that a hemispheric pattern of circulation is responsible for seasonal variations in the Earth's mesosphere.
\r\n\r\nWe summarize by noting the very different time scales for variations of CO in the upper atmospheres of Venus, the Earth, and Mars. The long diurnal period of Venus produces a very strong diurnal variation in mesospheric CO which is driven primarily by subsolar to antisolar circulation. CO in the terrestrial mesosphere shows strong seasonal variation which is apparently produced by seasonally driven meridional circulation. By contrast, if atmospheric CO does vary on Mars, it is most likely controlled by long-term changes in the chemistry and/or vertical mixing in the Martian atmosphere.
", "doi": "10.7907/mf7e-1581", "publication_date": "1983", "thesis_type": "phd", "thesis_year": "1983" }, { "id": "thesis:7466", "collection": "thesis", "collection_id": "7466", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:02062013-144652620", "primary_object_url": { "basename": "Jakosky_bm_1983.pdf", "content": "final", "filesize": 41355084, "license": "other", "mime_type": "application/pdf", "url": "/7466/1/Jakosky_bm_1983.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "The Seasonal Behavior of Water Vapor in the Mars Atmosphere", "author": [ { "family_name": "Jakosky", "given_name": "Bruce Martin", "orcid": "0000-0002-0758-9976", "clpid": "Jakosky-Bruce-Martin" } ], "thesis_advisor": [ { "family_name": "Ingersoll", "given_name": "Andrew P.", "orcid": "0000-0002-2035-9198", "clpid": "Ingersoll-A-P" }, { "family_name": "Muhleman", "given_name": "Duane Owen", "clpid": "Muhleman-D-O" } ], "thesis_committee": [ { "family_name": "Muhleman", "given_name": "Duane Owen", "clpid": "Muhleman-D-O" }, { "family_name": "Ingersoll", "given_name": "Andrew P.", "orcid": "0000-0002-2035-9198", "clpid": "Ingersoll-A-P" }, { "family_name": "Murray", "given_name": "Bruce C.", "clpid": "Murray-B-C" }, { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "Farmer", "given_name": "C. Bernard", "clpid": "Farmer-C-Bernard" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "Understanding the evolution of volatiles on Mars requires understanding the processes which are currently acting to cause exchange between the various reservoirs on annual and longer timescales. On the seasonal timescale, exchange of water can occur between the atmosphere and reservoirs of ice in the polar caps and of adsorbed water in the near-surface regolith covering the remainder of the planet. This exchange is driven by the seasonally-varying insolation and its consequent effects on the surface and subsurface temperatures and on the advance and retreat of the predominantly-CO2 polar caps. On a longer timescale, exchange can occur between these same reservoirs, and is driven by the changing annual insolation patterns which result from the 105-year timescale variations in Mars' orbital elements (predominantly the orbital obliquity). Observations of the seasonal water cycle and its variations from year to year from the Viking spacecraft and from Earth provide clues as to the importance of the various reservoirs and provide boundary conditions against which models of the various processes can be compared.
\r\n\r\nThe water vapor content of the Mars atmosphere was measured from the Viking Orbiter Mars Atmospheric Water Detectors (MAWD) for a period of more than one Martian year, from June, 1976, through April. 1979, and the results are presented here. The data reduction incorporates spatial and seasonal variations in surface pressure, and supplements earlier published versions of less-complete data. Column abundances vary between zero and about 100 precipitable microns (pr \u00b5m), depending on location and season, while the entire global abundance varies seasonally between an equivalent of about 1 and 2 km3 of ice. The first appearance of vapor at non-polar latitudes as northern summer approaches, and the drop in abundance at mid-latitudes as summer ends, both strongly imply the existence of a seasonal reservoir for water within the regolith. There appear to be no net annual sources away from the poles that contribute significant amounts of water. However, the strong annual gradient of vapor from north to south implies a net annual flow of vapor toward the south; this southward flow may be balanced in part by a northward flow during the global dust storms, by transport in the form of clouds or adsorbed onto dust grains, or during other years. The perennially-cold nature of the south-polar residual cap, along with the relatively large summertime vapor abundances over the cap, implies a net annual condensation of vapor onto the cap. Estimates are made of the southward transport, and are consistent with the movement of ice being important in the formation and evolution of the polar layered terrain, and with the formation of the individual layers at the rate of one per obliquity cycle (105 years).
\r\n\r\nThe global distribution of the annual average abundance of vapor is found to correlate well with Martian topography, as might be expected for a uniform constant atmospheric mixing ratio. If this topographic effect is divided out, the resulting residual map correlates with maps of surface albedo and thermal inertia; this correlation may be related to the control exerted by the surface and subsurface temperatures on the adsorption/desorption process and on the atmospheric temperature profile and, hence, the vapor holding capacity of the atmosphere.
\r\n\r\nThe vertical distribution of vapor within the atmosphere is inferred through comparison of the observed water vapor abundances with measurements of atmospheric temperatures. In order to not saturate, the vapor must be confined to the lowermost 1 to 3 scale heights (~ 10-30 km), with this height varying with location and season. Near-surface water vapor can condense out overnight and form a morning fog; estimates of the optical thickness of the resulting fog are made, and they agree well with observations of diurnal variations of opacity due to fog formation.
\r\n\r\nPrevious Earth-based near-infrared observations are re-interpreted here; they show that water ice condenses out onto the seasonal polar caps, but not during midday near the equator. Earth-based observations of the vapor column abundance are compared with the Viking MAWD results, and indicate that the seasonal cycle shows a remarkable repeatability, except during 1969 when large vapor abundances were present during southern summer. This difference is explained by postulating that all of the CO2 had sublimed off of the south residual cap that year, exposing the underlying water cap which would subsequently sublime and produce large amounts of atmospheric vapor; the rate and amount of CO2 sublimation may depend on the degree of dust storm activity each year and hence on the different thermal loads placed on the cap.
\r\n\r\nThe possible processes for producing seasonal changes in the atmospheric vapor abundances have been modeled in order to infer the relative importance of each process in the seasonal cycle. The equilibrium between water vapor and water adsorbed onto the regolith grains is sufficiently temperature-dependent that seasonal surface temperature variations are capable of driving a large exchange of water between the atmosphere and subsurface. For the likely range of regolith properties, this exchange is found to be from 10-150% of the observed seasonal change in atmospheric abundance; the differences between this exchange and the observed behavior result from transport of vapor due to the atmospheric circulation. Due to the latitudinal gradient of atmospheric vapor, there will also be a gradient of adsorbed water, with the south regolith containing much less water than that in the north; this gradient in the regolith will result independent of the vapor diffusivity in the regolith, as the near-surface water will be able to equilibrate on some timescale.
\r\n\r\nModels have been constructed which include regolith exchange, polar cap formation, and atmospheric transport. Comparison of the model results with the vapor observations and with other data regarding the physical nature of the surface allows constraints to be placed on the relative importance of each process. The models are capable of satisfactorily explaining the gross features of the observed behavior using plausible values for the regolith and atmosphere mixing terms. In the region between the polar caps, the regolith contributes as much water to the seasonal cycle of vapor as does transport in from the more-poleward regions, to within a factor of two. Globally, 10-50% of the seasonal cycle of vapor results from exchange of water with the regolith, about 40% results from the behavior of the residual caps, and the remainder is due to exchange of water with the seasonal caps. It is difficult to determine the relative importance of the processes more precisely than this because both regolith and polar cap exchange of water act in the same direction, producing the largest vapor abundance during the local summer. The system is ultimately regulated on the seasonal timescale by the polar caps, as the time to reach equilibrium between the atmosphere and regolith or between the polar atmosphere and the global atmosphere is much longer than the time for the polar caps to equilibrate with the local atmosphere. This same behavior will bold for longer timescales, with the polar caps being in equilibrium with the insolation as it changes on the obliquity timescale, and the atmosphere and regolith following along.
", "doi": "10.7907/f9fz-gg50", "publication_date": "1983", "thesis_type": "phd", "thesis_year": "1983" }, { "id": "thesis:16226", "collection": "thesis", "collection_id": "16226", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:10312023-202011054", "primary_object_url": { "basename": "Pechmann_JB_1983.pdf", "content": "final", "filesize": 66438934, "license": "other", "mime_type": "application/pdf", "url": "/16226/1/Pechmann_JB_1983.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Thermal Tides in the Atmosphere of Venus", "author": [ { "family_name": "Pechmann", "given_name": "Judith Burt", "clpid": "Pechmann-Judith-Burt" } ], "thesis_advisor": [ { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" } ], "thesis_committee": [ { "family_name": "Ingersoll", "given_name": "Andrew P.", "orcid": "0000-0002-2035-9198", "clpid": "Ingersoll-A-P" }, { "family_name": "Muhleman", "given_name": "Duane Owen", "clpid": "Muhleman-D-O" }, { "family_name": "Yung", "given_name": "Yuk L.", "orcid": "0000-0002-4263-2562", "clpid": "Yung-Y-L" }, { "family_name": "Harkrider", "given_name": "David G.", "clpid": "Harkrider-D-G" }, { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "The daily variation in the absorption of sunlight by the atmosphere provides the forcing for thermal tides. In this thesis the response of the Venus atmosphere as a function of height and latitude to the diurnal and semidiurnal components of the forcing is calculated using a linearized primitive equation model. We specify the atmospheric mean state using data from the Pioneer Venus probes and orbiter, and solve for the first order tidal perturbation. Our forcing function is based on data returned by the solar flux radiometer on the Pioneer Venus sounder probe. The perturbation variables are discretized horizontally by spherical harmonics and vertically by finite elements. A semi\u00ad implicit time-stepping algorithm is used.
\r\n\r\nThe model results for Venus thermal tides are in agreement with the solar-fixed component of diurnal and semidiurnal brightness temperature fluctuations determined from Pioneer Venus orbiter infrared radiometer (OIR) data. Contrary to the prediction of classical tidal theory, the observed semidiurnal brightness temperature maxima occur before the forcing maxima from about 60 to 80 km. In the model, this phase lead is due to a long vertical wavelength (~30 km) from the cloud tops to 80 km. Also, the data unexpectedly show that the semidiurnal amplitude is larger than the diurnal over much of the region observed, even though the diurna1 forcing is about twice as great. The model's diurnal temperature amplitude is larger than that observed in the brightness temperature. However, convolution with the OIR weighting functions results in model brightness temperature amplitudes which are as small as the observed values because the vertical wavelength of the\r\ndiurnal tide is shorter than the width of the weighting functions.
\r\n\r\nThe success of the model increases our confidence in our knowledge of the mean state of the Venus atmosphere and provides us with the opportunity to determine the importance of energy and angular momentum transport by the tides. The zonally averaged vertically integrated tidal energy flux is significant compared to the zonally averaged imbalance in incoming solar radiation and outgoing infrared radiation from equatorial to mid-latitudes. However, the tides do not in general tend to reduce the imbalance by transporting heat poleward. The mean meridional circulation driven by this imbalance and the tidal energy flux consists of stacked direct and indirect Hadley cells. The angular momentum transport is upward and poleward in the direct cells. Since the transport is not upward at all altitudes, some other processes must be involved in maintaining the large shear in the mean zonal wind. The vertical transport by the tides is small compared to that of the mean circulation. However, the tides do transport a significant amount of angular momentum equatorward from mid-latitudes.
", "doi": "10.7907/5cd0-3q63", "publication_date": "1983", "thesis_type": "phd", "thesis_year": "1983" }, { "id": "thesis:3101", "collection": "thesis", "collection_id": "3101", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-08122005-133355", "type": "thesis", "title": "Low-Thrust Perturbation Guidance", "author": [ { "family_name": "Bauer", "given_name": "Thomas Patrick", "clpid": "Bauer-Thomas-Patrick" } ], "thesis_advisor": [ { "family_name": "Caughey", "given_name": "Thomas Kirk", "clpid": "Caughey-T-K" } ], "thesis_committee": [ { "family_name": "Wood", "given_name": "Lincoln", "clpid": "Wood-L" }, { "family_name": "Culick", "given_name": "Fred E. C.", "clpid": "Culick-F-E-C" }, { "family_name": "Muhleman", "given_name": "Duane Owen", "clpid": "Muhleman-D-O" }, { "family_name": "Zukoski", "given_name": "Edward E.", "clpid": "Zukoski-E-E" }, { "family_name": "Caughey", "given_name": "Thomas Kirk", "clpid": "Caughey-T-K" } ], "local_group": [ { "literal": "GALCIT" }, { "literal": "div_eng" } ], "abstract": "Low-thrust perturbation guidance, as applied to the minimum time problem of an Earth to Mars rendezvous, has been reexamined and shown to perform orders of magnitude better, as measured by the terminal state error, than previous studies indicated. The orbits of Earth and Mars were assumed to be inclined and elliptical. The only forces considered were the Sun's gravity and that of the constant thrust rocket engine.
\r\n\r\nFirst order necessary conditions of the calculus of variations were developed for the nominal trajectory. The resulting nonlinear two-point boundary value problem was solved with the Backward Sweep Method. Feedback gain related and trajectory information is stored on a file during the optimization of the nominal trajectory to be retrieved later in the guidance programs by a high order interpolator.
\r\n\r\nTwo guidance schemes, Time-To-Go Guidance and Minimum Distance Guidance, were investigated for several initial perturbations in velocity and position. The performance of the two schemes was found to be clearly acceptable although not quite as good as reoptimization. The two schemes are equivalent in performance. Moreover, a simplified version of the schemes, Current Time Guidance, was found to be comparable in performance to the more elaborate guidance schemes.
\r\n\r\nA comparison of the current results with those of previous studies was made showing that terminal state errors can be reduced 100 to 10,000 times more than found earlier. This apparent improvement may possibly be explained by the use of a high fidelity integrator and other enhancements implemented in the software, although algorithm and programming mistakes in the earlier studies are suspected.
\r\n\r\nA similar minimum time problem, that of a two-dimensional Earth to Mars orbit transfer using a solar sail, was also reexamined. The optimized trajectory was found to be very similar to those obtained by most earlier studies. A recent report which prompted the study was found to have an error in a transversality condition causing anomalous results.
", "doi": "10.7907/TVQ3-FV70", "publication_date": "1982", "thesis_type": "phd", "thesis_year": "1982" }, { "id": "thesis:7458", "collection": "thesis", "collection_id": "7458", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:01302013-145914913", "primary_object_url": { "basename": "Cimino-jb-1982.pdf", "content": "final", "filesize": 27201697, "license": "other", "mime_type": "application/pdf", "url": "/7458/1/Cimino-jb-1982.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "The Composition, Vertical Structure and Global Variability of the Lower Cloud Deck on Venus as Determined by Radio Occultation Techniques", "author": [ { "family_name": "Cimino", "given_name": "Josephine Beatrice", "clpid": "Cimino-Josephine-Beatrice" } ], "thesis_advisor": [ { "family_name": "Ingersoll", "given_name": "Andrew P.", "orcid": "0000-0002-2035-9198", "clpid": "Ingersoll-A-P" } ], "thesis_committee": [ { "family_name": "Muhleman", "given_name": "Duane Owen", "clpid": "Muhleman-D-O" }, { "family_name": "Yung", "given_name": "Yuk L.", "orcid": "0000-0002-4263-2562", "clpid": "Yung-Y-L" }, { "family_name": "Shair", "given_name": "Fredrick H.", "clpid": "Shair-F-H" }, { "family_name": "Kliore", "given_name": "Arvydas J.", "clpid": "Kliore-Arvydas-J" }, { "family_name": "Elachi", "given_name": "Charles", "orcid": "009-0002-2156-967X", "clpid": "Elachi-C" }, { "family_name": "Ingersoll", "given_name": "Andrew P.", "orcid": "0000-0002-2035-9198", "clpid": "Ingersoll-A-P" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "The opportunity to determine the planetwide temperature and cloud structure of Venus using radio occultation techniques arose with Pioneer Venus. This orbiting spacecraft contained a dual frequency radio system which was used to collect radio occultation data for more than two years.
\r\n\r\nAmplitude and Doppler data provided by the radio occultation experiment provide a unique and powerful means of examining atmospheric properties in a region of Venus which may otherwise be observed only by means of a probe.
\r\n\r\nThe extraction of atmospheric properties from the received occultation data is a complicated non-linear process for which careful account of all contributing uncertainties must be taken. Such atmospheric phenomena as turbulence, oblateness due to winds, perturbations in the temperature, atmospheric density or gaseous composition affect both the Doppler and the amplitude data. Uncertainties inherent in the experiment itself and the data collection and processing procedures, such as trajectory errors, fluctuations in the power profile, averaging of the data and spacecraft wobble, result in additional uncertainties which must be considered.
\r\n\r\nAbsorption coefficient and temperature profiles were analyzed in detail for the effects of major sources of uncertainty. Inasmuch as the power loss due to refractive defocussing is determined from the Doppler data, uncertainties in the refractivity as well as the received power are considered. Power fluctuations are found to produce the greatest uncertainty in the S-band absorption coefficient profiles. Power fluctuations and spacecraft wobble contribute the greatest uncertainty to the X-band data. In fact, in many cases the spacecraft wobble has rendered the X-band data useless.
\r\n\r\nAbsorption due to gaseous components of the atmosphere are subtracted from the measured absorption coefficient profiles before they are used to compute cloud mass contents. The H2O mixing ratio profile used is that measured by the Venera 11 and 12 spectrophotometers. The SO2 profile was determined from the Venera 11 and 12 and Pioneer probe gas chromatograph and mass spectrometer results. The sulfuric acid saturation vapor mixing ratio used is the equilibrium vapor pressure above a concentrated sulfuric acid-water solution at the temperatures of the lower cloud deck.
\r\n\r\nThe absorption due to the gaseous components is found to represent a small part of the total absorption. In the main cloud deck, gaseous absorption contributes 10 to 20% and at the bottom of the detected absorption layer the sulfuric acid vapor contributes 60 to 100% to the absorption due to increased acid vapor pressures resulting from higher temperatures in this region. The clouds are the primary contributing absorbers in the 1 to 3 bar level of the Venus atmosphere. Below about 3 bars, absorption due to sulfuric acid vapor dominates.
\r\n\r\nAs a first attempt, mass content profiles were produced from the absorption coefficient data assuming the clouds were composed of concentrated sulfuric acid-water liquid. The resulting mass contents were on the order of several grams per cubic meter. Although planetwide variability in the lower cloud deck may account for differences in these radio occultation mass contents and those determined by the Pioneer probes, a second factor discounting purely liquid clouds has arisen. The dielectric constants of liquid sulfuric acid were measured in the laboratory at S-and X-band wavelengths and the results suggest the wavelength dependence for absorption by the liquid is 1/\u03bb2. The wavelength dependence measured by the radio occultation experiment is about 1/\u03bb1.2. In addition, the wavelength dependence required to fit the opacity determined from the 1.35 cm microwave emission data is 1/\u03bb1.2 to 1/\u03bb1.5. Apparently the liquid sulfuric acid droplet model does not satisfy the observed wavelength dependence or mass content.
\r\n\r\nIf, however, a cloud particle model consisting of a solid non-absorbing dielectric sphere with a concentric liquid sulfuric acid coating is invoked, the absorptivity of the particles increases and the mass content derived from the absorption coefficient profiles decreases. As the ratio of the core radius to the total radius (q) increases, absorption increases by more than a factor of 10 for high values of q. In the case of pure sulfuric acid droplets, the conductivity is sufficiently high that some of the field is excluded from the interior of the droplet thereby reducing the absorption. When a dielectric core of nonabsorbing material is introduced, two effects occur which contribute to the increase in the electric field which penetrates the drop. First, the relative volume filled by sulfuric acid decreases and the number of available free charges decreases. Second, the dielectric core, which is also polarized in the presence of the electric field, affects the arrangement of the free charges by attracting them to the inner surface and by acting as a barrier in the presence of the rapidly alternating electric field.
\r\n\r\nThe mass contents for all orbits in the equatorial region of Venus are calculated using values of q of from 0 to 1. The resulting profiles match the probe mass content profiles at similar locations when a q of 0.98 is chosen. Values for q of 0.97 to 0.99 change the absorptivity of the cloud particles by as much as 50%.
\r\n\r\nThe Wavelength dependence of the absorption for the spherical shell model varies with q from 1/\u03bb2 for pure liquid to \u03bb0.2 for a large core. A q of 0.98 results in a wavelength dependence of 1/\u03bb1.0 to 1/\u03bb1.4. which matches the radio occultation absorption wavelength dependence and the microwave opacity wavelength dependence.
\r\n\r\nMass content profiles using a q of 0.98 were determined for occultations in the polar, collar, midlatitudinal and equatorial regions assuming q remains constant over the planet. The results show considerable variability in both the level and the magnitude of the lower cloud deck. The cloud layer is lowest in altitude in the polar region. This might be expected as the temperature profile is cooler in the polar region than over the rest of the planet. The mass content is greatest in the polar and collar regions; however, many of the collar profiles are cut off due to fluctuations resulting from increased turbulence in the collar region. The mass contents are least dense in the midlatitude regions.
\r\n\r\nThese results support the value of using radio occultation techniques to obtain temporal and spatial coverage of the planet Venus in terms of cloud composition and mass content.
\r\n\r\n", "doi": "10.7907/j7et-kc02", "publication_date": "1982", "thesis_type": "phd", "thesis_year": "1982" }, { "id": "thesis:7473", "collection": "thesis", "collection_id": "7473", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:02122013-101424216", "type": "thesis", "title": "Large Impact Craters and Basins: Mechanics of Syngenetic and Postgenetic Modification", "author": [ { "family_name": "McKinnon", "given_name": "William Beall", "clpid": "McKinnon-William-Beall" } ], "thesis_advisor": [ { "family_name": "Melosh", "given_name": "H. Jay", "orcid": "0000-0003-1881-1496", "clpid": "Melosh-H-J" } ], "thesis_committee": [ { "family_name": "Melosh", "given_name": "H. Jay", "orcid": "0000-0003-1881-1496", "clpid": "Melosh-H-J" }, { "family_name": "Ingersoll", "given_name": "Andrew P.", "orcid": "0000-0002-2035-9198", "clpid": "Ingersoll-A-P" }, { "family_name": "Muhleman", "given_name": "Duane Owen", "clpid": "Muhleman-D-O" }, { "family_name": "Shoemaker", "given_name": "Eugene Merle", "clpid": "Shoemaker-E-M" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "The impact crater is the ubiquitous landform of the solar system. Theoretical mechanical analyses are applied to the modification stage of crater formation, both syngenetic (immediate or short term) and postgenetic (long term).
\r\n\r\nThe mechanical stability of an impact crater is analyzed via a quasi-static, axisymmetric slip line theory of plasticity. The yield model incorporated is Mohr-Coulomb and a simplified rectangular profile is used for the transient cavity. The degree of stability (or instability) is described as a function of internal friction angle, depth/diameter ratio, and a dimensionless parameter \u03c1gH/c (\u03c1 = density, g = acceleration of gravity, H = depth, and c = cohesion strength). To match the observed slumping of large lunar craters the cohesion strength of the lunar surface material must be low (<20 bars) and the angle of internal friction must be less than 2\u00b0. It is not implausible that these failure strength characteristics are realized by freshly shocked rock. A theoretical description of impact crater collapse is evolved which accounts for the development of wall scallops, slump terraces, and flat floors. A preliminary set of scale model experiments performed in a centrifuge corroborate the theory. The strength of terrestrial planet surfaces under impact is seen to vary by as much as a factor of two.
\r\n\r\nShortly after the excavation of a large impact crater the transient cavity collapses, driven by gravity. It is shown that at least one concentric fault scarp forms about the crater, if the strength of the target material decreases sufficiently rapidly with increasing depth. This is demonstrated by two classes of models: extrusion flow models which assume a weak layer underlying a strong layer, and plastic flow models which assume a continuous decrease of cohesion strength with depth. Both classes predict that the ratio of the radius of the scarp to the transient crater radius is between 1.2 and 2 for large craters.
\r\n\r\nLarge impact basins on Ganymede and Callisto are characterized by one or more concentric rings or scarps. The number, spacing, and morphology of the rings is a function of the thickness and strength of the lithosphere, and crater diameter. When the lithosphere is thin and weak, the collapse is regulated by flow induced in the asthenosphere. The lithosphere fragments in a multiply concentric pattern (e.g., Valhalla, Asgard, Galilee Regio, and a newly discovered ring system on Callisto). The thickness and viscosity of a planetary lithosphere increases with time as the mantle cools. A thicker lithosphere leads to the formation of one (or very few) irregular normal faults concentric to the crater (e.g., Gilgamesh). A gravity wave or tsunami induced by impact into a liquid mantle would result in both concentric and radial extension features. Since these are not observed , this process cannot be responsible for the generation of the rings around the basins on Ganymede and Callisto. The appearance of Galilee Regio and portions of Valhalla is best explained by ring graben, and though the Valhalla system is older, the lithosphere was 1.5-2.0 times as thick at the time of formation. The present lithosphere thickness is too great to permit development of any rings.
\r\n\r\nIt has been proposed that a mascon may be in the form of an annulus surrounding the Caloris basin on Mercury, associated with the smooth plains. The effects (stresses, deformation, surface tectonic style, gravity anomalies, etc.) of such a ring load on a floating elastic lithosphere of variable thickness are investigated. The main characteristics of the surface tectonic pattern are normal faulting within the basin and thrust faulting beneath the ring load both in agreement with observation Moreover, the dominant concentric trend of the basin normal faults is consistent with the ring load hypothesis provided the mercurian lithosphere was \u2264125 km thick at the time of faulting. Simple updoming within the basin would produce normal faults of predominantly radial orientation.
", "doi": "10.7907/1ehb-nm16", "publication_date": "1981", "thesis_type": "phd", "thesis_year": "1981" }, { "id": "thesis:3231", "collection": "thesis", "collection_id": "3231", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-08262008-113619", "type": "thesis", "title": "The Structure of Hydroxyl Masers and Circumstellar Envelopes of Long Period Variable Stars", "author": [ { "family_name": "Reid", "given_name": "Mark Jonathan", "orcid": "0000-0001-7223-754X", "clpid": "Reid-Mark-Jonathan" } ], "thesis_advisor": [ { "family_name": "Muhleman", "given_name": "Duane Owen", "clpid": "Muhleman-D-O" } ], "thesis_committee": [ { "family_name": "Muhleman", "given_name": "Duane Owen", "clpid": "Muhleman-D-O" }, { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" }, { "family_name": "Neugebauer", "given_name": "Gerry", "clpid": "Neugebauer-G" }, { "family_name": "Preston", "given_name": "George W.", "clpid": "Preston-G-W" }, { "family_name": "Cohen", "given_name": "Marshall H.", "clpid": "Cohen-M-H" } ], "local_group": [ { "literal": "Owens Valley Radio Observatory (OVRO)" }, { "literal": "Astronomy Department" }, { "literal": "div_pma" } ], "abstract": "Long period variable stars with envelopes of circumstellar dust and gas often exhibit strong hydroxyl (OH) maser emission. This emission is characterized by two emission line complexes typically separated by 20 km/s. While the OH maser spectra suggest well defined dynamical properties of the circumstellar material, the crucial observations required to determine these properties have been lacking. This thesis is primarily concerned with determining the radial velocity of the central star and the spatial distribution of the maser emission in the circumstellar material.
\r\n\r\nThe radial velocity of the central star can be determined by a statistical analysis of spectral line velocities in an ensemble of stars. Such an analysis is presented in Chapter I for optical emission and absorption lines and for radio OH maser emission lines. The results indicate that, contrary to currently accepted theories, the optical absorption line velocities and the high velocity OH emission line velocities are red-shifted with respect to the stellar radial velocity. This argues against models of the OH emission which involve shock fronts or emission from the limb of a spherically expanding circumstellar shell.
\r\n\r\nThe spatial distribution of the maser emission can be determined from radio interferometric observations. Spectral-line very long baseline (VLB) interferometric observations of the OH maser emission in long period variable stars such as IRC+F10011, U Ori and R Aql are presented in Chapter II. The primary result of these observations is that the apparent sizes of the OH maser components in long period variable stars are greater than or about 5 x 1015 cm. These large apparent sizes argue strongly against either gravitational collapse or rotation as the dominant dynamical process in the circumstellar envelope. Analysis of data obtained on IRC+10011 and VY CMa (discussed in Chapter III) indicate that the two emission complexes probably are separated by distances less than, or comparable to, the extent of the emission in either complex. These and other findings suggest that OH emission from long period variable stars comes from a series of concentric, inhomogeneous, circumstellar shells expanding from the central star. The origin of these shells is probably a result of condensation of dust followed by radiative acceleration away from the star during the stellar light cycle.
\r\n\r\nA direct Fourier inversion of VLB data is presented in Chapter III for the 1612 MHz OH emission of VY CMa. This is the first attempt at such an analysis procedure for any VLB observations. This work demonstrates that Fourier inversion of spectral-line VLB data, even with very limited u-v coverage, is more efficient and less biased than direct model fitting for the resolution of complex source structures.
\r\n", "doi": "10.7907/4EGT-TW53", "publication_date": "1976", "thesis_type": "phd", "thesis_year": "1976" }, { "id": "thesis:14017", "collection": "thesis", "collection_id": "14017", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:12072020-234014838", "primary_object_url": { "basename": "Lagus_PL_1974.pdf", "content": "final", "filesize": 30518048, "license": "other", "mime_type": "application/pdf", "url": "/14017/1/Lagus_PL_1974.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "The Equations of State of Hydrogen and Argon: Applications to the Jovian Interior", "author": [ { "family_name": "Lagus", "given_name": "Peter Leonard", "clpid": "Lagus-Peter-Leonard" } ], "thesis_advisor": [ { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" } ], "thesis_committee": [ { "family_name": "Archambeau", "given_name": "Charles B.", "clpid": "Archambeau-C-B" }, { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" }, { "family_name": "Muhleman", "given_name": "Duane Owen", "clpid": "Muhleman-D-O" }, { "family_name": "Anderson", "given_name": "Donald L.", "clpid": "Anderson-D-L" }, { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "Hugoniot data for solid argon (initially at 77\u00b0K and l bar) and solid hydrogen (initially at 5\u00b0K and 1 bar) have been obtained to 143 kbar and 6.4 kbar respectively utilizing a propellant gun. The argon data (at volumes of 15.28, 14.84 and 14.64 cc/mole) are in fair agreement with previous shock data, and in excellent agreement with recent theoretically predicted Hugoniots. The hydrogen data (at volumes of 17.10, 15.32, 15.27, 15.11 cc/mole) are compared with Hugoniots calculated from published isothermal compression data. For both argon and hydrogen, the present data are consistent with the assumption that \u03b3/V is constant. Furthermore, to compressions of V/V\u2080 \u2243 0.65, no gross inconsistencies exist between shock-wave and isothermal compression measurements in solid hydrogen.
\r\n\r\nA simple equation of state (E0S) for molecular hydrogen based on a spherically averaged De Boer-type repulsion potential which explicitly includes the zero point energy reproduces experimental pressure-volume data between 5 kbar and 370 kbar. This molecular equa\u00adtion of state when combined with recent metallic equations of state implies a molecular to metallic phase transition pressure of 1.9 \u00b1 0.4 Mbar at 0\u00b0K.
\r\n\r\nA thermally expanded model of Jupiter which incorporates this molecular equation of state, recent metallic hydrogen and helium equa\u00adtions of state, and a van der Waals-type atmosphere yields a model with a hydrogen abundance of x = 0.57. However, the interior temperatures are everywhere above the melting temperature of metallic hydrogen.
", "doi": "10.7907/zzpq-2876", "publication_date": "1974", "thesis_type": "phd", "thesis_year": "1974" } ]