The main theme of this work is the development of a simplified model of the martian circulation suitable for conducting computationally fast long term simulations of the martian climate system. In particular, we are looking for causes of the irregular occurrence of the martian global dust storms (GDSs). The low-order model (LOM) is constructed by Galerkin projection of a 2D (zonally averaged) general circulation model (GCM) onto a truncated set of basis functions. The resulting low-order model consists of twelve coupled nonlinear ordinary differential equations (ODEs). The forcing of the model is described by simplified physics based on Newtonian cooling and Rayleigh friction. The atmosphere and surface are coupled: atmospheric heating depends on the dustiness of the atmosphere, and the surface dust source depends on the strength of the atmospheric winds. Parameters of the model are tuned to fit output of the NASA Ames GCM.
\r\n\r\nThe model performance is examined for different seasons and dust opacities and it is found that the simulated mean meridional circulation and temperature fields compare well with the more sophisticated GCM. The time of occurence and duration of the global dust storms produced by the model compare well with observations by Viking Landers (VLs). The intensity of the meridional circulation as simulated by the LOM during northern summer is stronger than that predicted by the GCM. The situation can be improved if the Rayleigh friction varies seasonally. The LOM uncoupled from the dust source can be further simplified to form the Lorenz system with forcing.
\r\n\r\nThe model is applied to the problem of interannual variability of martian global dust storms. Basic hypotheses of the intrinsic and of the extrinsic irregularity of the martian climate system are tested. The intrinsic irregularity hypothesis implies that the system under consideration is chaotic, so that small variations in initial conditions make the behavior of the system essentially unpredictable. Different paths taken by the system in state space would correspond to years with and without a GDS. The extrinsic irregularity hypothesis, on the other hand, implies that without noise the system behaves periodically, but stochastic forcing of the system causes it to behave irregularly. It is concluded that the observed variability of GDSs is more easily explained by extrinsic irregularity. The stochastic forcing (``noise') could be provided by transient weather systems or some surface process, like size sorting or redistribution of the sand particles in the ``active' (i.e., storm generating) zones on the surface. The results are very sensitive to the value of the saltation threshold, which hints at the possible feedback between saltation threshold and dust storm activity. According to this hypothesis, the saltation threshold has adjusted its value so that dust storms are barely able to occur.
", "doi": "10.7907/MGSA-ZT98", "publication_date": "2001", "thesis_type": "phd", "thesis_year": "2001" }, { "id": "thesis:7459", "collection": "thesis", "collection_id": "7459", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:01302013-163300566", "primary_object_url": { "basename": "Ivanov 2000.pdf", "content": "final", "filesize": 29499701, "license": "other", "mime_type": "application/pdf", "url": "/7459/1/Ivanov 2000.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Some aspects of the Martian climate in the Mars Orbiter Laser Altimeter (MOLA) investigation. Part I. Evolution of the polar residual ice caps. Part II. Polar night clouds. Part III. Interpretation of the MOLA reflectivity measurement in terms of the surface albedo and atmospheric opacity", "author": [ { "family_name": "Ivanov", "given_name": "Anton Borisovich", "clpid": "Ivanov-A-B" } ], "thesis_advisor": [ { "family_name": "Muhleman", "given_name": "Duane Owen", "clpid": "Muhleman-D-O" } ], "thesis_committee": [ { "family_name": "Unknown", "given_name": "Unknown" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "The spacecraft exploration of the planet Mars in the last two decades provided scientists\r\nwith an enormously rich data base. This work presents some aspects of the\r\nMars Orbiter Laser Altimeter investigation related to the issues in the Martian climatology.\r\nThe instrument continues to function on board of the Mars Global Surveyor\r\nSpacecraft.
\r\n\r\nThe polar ice caps on Mars are the largest reservoirs of water on the planet.\r\nTheir formation and evolution are not understood very well at this point. Ice flow,\r\nsublimation and wind erosion are believed to be the most important processes that\r\nshape the caps. We have developed a model to understand the role of sublimation\r\nfor the formation of the ice caps and attempted to constrain the time scale for the\r\nformation of the observed ice caps. The model has been justified using the precise\r\ntopography of the ice caps and the layered terrains that have been measured by the\r\nMOLA instrument. We argue that sublimation is a very important process for the\r\nformation of the caps, especially on the time scales greater than 10 million years.
\r\n\r\nWe report the direct observations of CO_2 clouds, forming during the polar winter\r\ntimes over both poles. These clouds are similar over both poles and possibly represent\r\na CO_2 snowfall. On the basis of the reflective properties and spatial occurrence, we\r\ncan distinguish two major classes of clouds. We will discuss some hypotheses on the\r\nmechanisms of their formation.
\r\n\r\nTotal atmospheric opacity of the Martian atmosphere at 1\u00b5m can be derived\r\nfrom the MOLA reflectivity measurement. Opacity estimates for the period from\r\nL_S = 105\u00b0 to L_S = 220\u00b0 are found to be consistent with the Viking Lander and\r\nPathfinder values. Opacity measured in the polar regions displays storms and polar\r\nhood activity. Aerosol scale heights can be inferred from the opacity changes on some\r\nlarge scale topographic features. Dust scale heights are found to be lower than the\r\natmospheric scale height. Water ice cloud scale heights are found to be consistent with the atmospheric scale height. Comparison of the MOLA derived opacity with\r\nthe TES derived opacity yields information on the aerosol particle size distribution.\r\nWe discuss an algorithm to derive 1\u00b5m normal albedo of the surface. 9\u00b5m dust\r\nopacity from the Thermal Emission Spectrometer (TES) is employed to remove an\r\natmospheric attenuation from the MOLA reflectivity measurements. We will present\r\nsome initial results on the calculation of the surface albedo.
\r\n", "doi": "10.7907/9mv8-hz72", "publication_date": "2000", "thesis_type": "phd", "thesis_year": "2000" }, { "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:7448", "collection": "thesis", "collection_id": "7448", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:01282013-095417825", "primary_object_url": { "basename": "Kursinski_er_1997.pdf", "content": "final", "filesize": 68499506, "license": "other", "mime_type": "application/pdf", "url": "/7448/1/Kursinski_er_1997.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "The GPS Radio Occultation Concept: Theoretical Performance and Initial Results", "author": [ { "family_name": "Kursinski", "given_name": "Emil Robert", "clpid": "Kursinski-Emil-Robert" } ], "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": "Yung", "given_name": "Yuk L.", "clpid": "Yung-Y-L" }, { "family_name": "Ingersoll", "given_name": "Andrew P.", "clpid": "Ingersoll-A-P" }, { "family_name": "Clayton", "given_name": "Robert W.", "clpid": "Clayton-R-W" }, { "family_name": "Anderson", "given_name": "Donald L.", "clpid": "Anderson-D-L" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "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:7464", "collection": "thesis", "collection_id": "7464", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:02052013-152025528", "primary_object_url": { "basename": "Gurwell 1996.pdf", "content": "final", "filesize": 32321111, "license": "other", "mime_type": "application/pdf", "url": "/7464/1/Gurwell 1996.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Planetary atmospheres: probing structure through millimeterwave observations of carbon monoxide", "author": [ { "family_name": "Gurwell", "given_name": "Mark Andrew", "clpid": "Gurwell-M-A" } ], "thesis_advisor": [ { "family_name": "Muhleman", "given_name": "Duane Owen", "clpid": "Muhleman-D-O" } ], "thesis_committee": [ { "family_name": "Unknown", "given_name": "Unknown" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "This thesis consists of inteferometric observation of carbon monoxide from\r\nthree planetary atmospheres. The observations address specific questions about the\r\nstate and structure of each atmosphere. The analysis and results for each planetary\r\nbody are contained within individual chapters of the thesis and the abstract for each\r\nis reproduced below.
\r\n\r\nTitan: Evidence for Well-Mixed Vertical Profile
\r\n\r\nWe report on new millimeter heterodyne observations of the ^(12)CO J(1 - 0)\r\nrotational transition from the stratosphere of Titan made in October 1994 with the\r\nOwens Valley Radio Observatory Millimeter Array. The spectrum obtained clearly\r\nexhibits a strong emission core over the ~600 MHz bandwidth of the upper sideband\r\nspectrometer. The lineshape, referenced to the flat spectrum simultaneously observed\r\nin the lower sideband was inverted to determine a best fit CO mixing ratio profile\r\nconsistent with the observations. The bet fit profile is a constant mixing ratio of 5 \u00b1 1 x 10^(-5) over the altitude range of 60- 200 km. Combined with IR observation\r\nof tropospheric CO (\u0192co = 6 x 10^(-5), Lutz et al. 1983) this provides strong evidence\r\nthat CO is well mixed from the surface to at least 200 km in Titan\u2019s atmosphere.
\r\n\r\nMars: Thermal Structure from 0-70 km
\r\n\r\nMillimeter-wave heterodyne observations of the ^(12)CO J (l - 0) rotational transition\r\nfrom the atmosphere of Mars were made on three dates in February 1993 with\r\nthe Owens Valley Radio Observatory Millimeter Array. These observations yielded\r\nhigh-quality spectra with a spatial resolution of 4.2\" on a 12.5\" diameter Mars. The\r\nspectra were numerically inverted for profiles of the local atmospheric temperature\r\nfrom 0 to 70 km, assuming a constant CO mixing ratio for the atmosphere. The\r\nderived average low latitude atmospheric temperature profile is approximately 20 K\r\ncooler than reference temperature profiles compiled during the Viking era. This new\r\ntemperature profile is well-matched by cooler profiles determined from whole disk CO\r\nmeasurements, suggesting very little dust loading of the atmosphere at the time of\r\nthe observations (Clancy et al. 1990). In addition, the revealed thermal structure\r\nshows variation with latitude, and these temperature profiles compare well with profiles\r\nderived from Mariner 9 IRIS observations (Leovy 1982, Santee and Crisp 1993) and calculated thermal structure from the Mars General Circulation Model (Haberle\r\net al.. 1993). The temperature profiles were averaged in local time and the resulting\r\ncross-section of temperature as a function of pressure and latitude used to infer the\r\nmean zonal circulation of the atmosphere. These wind results are somewhat compromised\r\nby the relatively low spatial resolution of the observation but do qualitatively\r\nmatch both inferred zonal winds from the Mariner 9 IRIS observations and Mars\r\nGCM calculations. These initial observations point toward the desirability of further\r\ninterferometric measurements.
\r\n\r\nVenus: Temporal Variations of the Mesophere
\r\n\r\nMillimeter-wave heterodyne observations of the ^(12)CO J(1-0) rotational transition\r\nfrom the mesosphere of Venus were made in early November and early December\r\n1994 with the Owens Valley Radio Observatory Millimeter Array. The spatial resolute ion for each day was about 1000 km at the sub-earth point. The high quality CO\r\nspectra were numerically inverted for profiles of the local CO mixing ratio from 80\r\nto 105 km, assuming a Pioneer Venus mean temperature profile for the atmosphere.\r\nFor each day the revealed CO distribution shows a nightside maximum centered at\r\nlow latitudes and shifted from the anti-solar point toward the morning terminator.\r\nBoth clays show a clear latitudinal falloff in the CO abundance. In November the\r\nmaximum was centered at roughly 2^h local time at 100 km, while in December the\r\nmaximum was at roughly 4 \u2013 4.5^h local time at 100 km. In addition, CO abundances\r\nwere slightly higher in November. The changes in the CO distribution are\r\nexamined in the context of the mesospheric circulation model of Clancy and Muhleman\r\n(1985b). The increased shift away from the anti-solar point and decreased CO\r\nabundance for the December observations both point toward increased zonal and/or\r\ndecreased sub-solar to anti-solar circulation within the mesosphere during the month\r\nbetween observations.
\r\n", "doi": "10.7907/wbs1-8j46", "publication_date": "1996", "thesis_type": "phd", "thesis_year": "1996" }, { "id": "thesis:7467", "collection": "thesis", "collection_id": "7467", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:02062013-163011023", "primary_object_url": { "basename": "Weisstein 1996.pdf", "content": "final", "filesize": 37142774, "license": "other", "mime_type": "application/pdf", "url": "/7467/1/Weisstein 1996.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Millimeter/submillimeter fourier transform spectroscopy of Jovian planet atmospheres", "author": [ { "family_name": "Weisstein", "given_name": "Eric W.", "clpid": "Weisstein-E-W" } ], "thesis_advisor": [ { "family_name": "Muhleman", "given_name": "Duane Owen", "clpid": "Muhleman-D-O" } ], "thesis_committee": [ { "family_name": "Unknown", "given_name": "Unknown" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "A new Fourier transform spectrometer, built for use at the Caltech Submillimeter\r\nObservatory, has been used to observe all four of the jovian planets (Jupiter,\r\nSaturn, Uranus, and Neptune) in the millimeter-submillimeter wavelength range (0.3-\r\n3.0 mm). The observations have resulted in the detection of the PH_3 1 - 0 rotational\r\nline (266.9 GHz) in Saturn. and the PH_3 3 - 2 ( 800.5 GHz) line in both Jupiter and\r\nSaturn. Because PH_3 is a disequilibrium species, it is an important tracer of vertical\r\nmixing and upper atmospheric photochemistry, and can therefore be used to derive\r\ndynamical and chemical properties of the jovian atmospheres. A jovian planet radiative transfer code has been used to model the observed PH_3 lineshapes. Using the\r\nFTS, a spectral line survey covering the entire range of submillimeter frequencies observable from the ground has also been performed on Jupiter at Saturn at a resolution\r\nof 200 MHz. This survey has yielded the tentative detection of HCl (and possibly\r\nHCN) in Saturn and, again with the aid of radiative transfer modeling, provided a\r\ngreat number of improved upper limits on the concentrations of many other species.\r\nFinally, Uranus and Neptune have been observed in the 1300 \u00b5m atmospheric window\r\nwhich contains the CO 2 - 1 transition. This line was not detected in either planet,\r\nplacing upper limits on the tropospheric CO mole fraction of 0.5 ppm in Uranus and\r\n1.4 ppm in Neptune.\r\n", "doi": "10.7907/R90F-8A53", "publication_date": "1996", "thesis_type": "phd", "thesis_year": "1996" }, { "id": "thesis:6683", "collection": "thesis", "collection_id": "6683", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:09222011-102938775", "primary_object_url": { "basename": "Hofstadter_md_1992.pdf", "content": "final", "filesize": 36395418, "license": "other", "mime_type": "application/pdf", "url": "/6683/1/Hofstadter_md_1992.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Microwave observations of Uranus", "author": [ { "family_name": "Hofstadter", "given_name": "Mark David", "orcid": "0000-0002-3208-3918", "clpid": "Hofstadter-Mark-David" } ], "thesis_advisor": [ { "family_name": "Muhleman", "given_name": "Duane Owen", "clpid": "Muhleman-D-O" } ], "thesis_committee": [ { "family_name": "Unknown", "given_name": "Unknown" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "This thesis explores the atmosphere of Uranus using microwave observations at wavelengths from 1 to 20 cm, with primary emphasis on high resolution VLA data at wavelengths\r\nof 2 and 6 cm. While radio maps of Uranus have been published previously, this is the first detailed analysis and interpretation of such observations. Atmospheric\r\nstructures are mapped to depths greater than has been seen on any giant planet. Several features of the data are immediately clear. First, there are strong horizontal and vertical gradients in the atmospheric properties that control the radio brightness. Polar regions are much brighter than lower latitudes, and the deep troposphere (pressures greater than a few tens of bars) appears much dimmer than would be expected based on the upper troposphere.\r\n(Both these results had been postulated in previous works, but older observations lacked the resolution to confirm them.) A second important feature of the data is that the\r\nintrinsic latitudinal brightness variations determined in this work at 2 cm and 6 cm are highly correlated with each other and with Voyager infrared measurements, suggesting a\r\ncommon cause. Because these data sets probe different altitudes between 50 and 0.1 bar, the cause must be acting over this altitude range of about 250 km. Another immediate\r\nresult, independent of atmospheric modeling, is that the radio brightness features have not changed significantly in the 8 years between 1981 and 1989.
\r\n\r\nSince radio brightness is a function of temperature and composition, the observations can be used to map these properties as a function of latitude and height. Arguments are presented that indicate compositional gradients are the dominant factor controlling the brightness variations, and these compositional changes are used as a tracer to infer the general circulation and some of the chemical processes of the atmosphere. The most likely interpretation of the data is that the Southern Hemisphere is dominated by a single meridional circulation cell, with an upwelling centered near -25\u00b0 latitude that brings absorber rich air parcels from 50 bars up to the 0.1 bar region. As parcels rise, the absorber mixing ratio drops by a factor of about 100 between 25 and 10 bars, and then a further factor of 2 at higher altitudes. These depletions are probably due to condensation. The absorber depleted parcels then move poleward and descend, dominating the atmospheric\r\ncomposition over the pole down to 50 bars, but not deeper. This circulation is consistent with the zonal winds and upper atmospheric temperatures observed by Voyager in the\r\ncontext of a simple, linear, dynamical model. The model suggests that the forcing driving these motions occurs within the upper few hundred bars of the atmosphere. The species most likely to be responsible for microwave absorption in the atmosphere is NH_3, and at depth it appears to have a molar mixing ratio within an order of magnitude of 1.4 x 10^(-4), the solar value. The formation of an NH_4SH cloud above 30 bars can account for the\r\nprimary depletion of NH_3, while NH_3 ice condensation at 5 bars accounts for the rest. Most of the results discussed here, however, are independent of what the absorbing\r\nspecies actually is.
\r\n\r\nSuperimposed on the large scale brightness pattern are smaller brightness oscillations, less than about 15\u00b0 wide in latitude. These long lasting features are reminiscent of the zones and belts of Jupiter, and could be the result of variations in either cloud altitudes or the depth of penetration of subsiding air parcels. A more extensive analysis is needed, however, to understand these small scale structures. The final point addressed in this\r\nwork is the seasonal variability of the atmosphere. While no variations exist in the current high resolution data set, which covers about 10 years of the mid-summer season,\r\nit is expected that detectable changes will occur over 20 to 40 year time scales (each season on Uranus lasts 21 years). The magnitude of the variations, however, cannot be\r\ndetermined from the available data.
", "doi": "10.7907/9RTG-Q786", "publication_date": "1992", "thesis_type": "phd", "thesis_year": "1992" }, { "id": "thesis:6703", "collection": "thesis", "collection_id": "6703", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:10042011-095138905", "primary_object_url": { "basename": "Shah_kp_1992.pdf", "content": "final", "filesize": 36106813, "license": "other", "mime_type": "application/pdf", "url": "/6703/1/Shah_kp_1992.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Interferometric observations of the J(0,1) CO line on Venus: upper Mesospheric winds and CO abundance", "author": [ { "family_name": "Shah", "given_name": "Kathryn Pierce", "clpid": "Shah-K-P" } ], "thesis_advisor": [ { "family_name": "Muhleman", "given_name": "Duane Owen", "clpid": "Muhleman-D-O" } ], "thesis_committee": [ { "family_name": "Ingersoll", "given_name": "Andrew P.", "clpid": "Ingersoll-A-P" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "In 1988, we observed Venus with the millimeter\r\ninterferometer at the Owens Valley Radio Astronomy\r\nObservatory at 115.2712 GHz, the first rotational transition\r\nof ^(12)CO. The 33.\"4 diameter disk was spatially resolved by a synthesized beam with a full-width-half-maximum of 2.\"8. Local time ranged from afternoon on the planetary eastern limb, 2 PM, to just past local midnight on the western limb, 12:30 AM. Venus' millimeter continuum emission was measured in a 400 MHz broadband channel. More\r\nimportantly, the CO absorption line was measured and finely resolved in frequency by two 32-channel filterbanks having channel widths of 50 kHz and 1 MHz.
\r\n\r\nThe 400 MHz broadband channel visibility data yielded a continuum brightness map of Venus. Brightness variations across the disk were primarily caused by sidelobe beam effects associated with the incomplete (u,v) coverage of the OVRO array. However, after radial averaging, the\r\ncontinuum brightness map continued to show one significant trend - a nightside limb cooler than the dayside limb. The\r\ncontinuum channel has a weighting function which samples a wide layer in the atmosphere between 40-60 km at normal incidence and 55-75 km along the planet limb. A radiative transfer model roughly reproduced the increased nightside limb-darkening, when given a mesospheric temperature profile 40 K cooler than the nominal Pioneer Venus nightside temperature profile between 60-85 km. The strength of this result is undercut-by strong uncertainties associated with the continuum map's absolute intensity values due to the small number of baselines in the OVRO array.
\r\n\r\nThe 50 KHz filterbank resolved the inner core of the CO absorption line. This yielded the first measurement of doppler shifts across Venus due to strong winds in the\r\nupper mesosphere. It is the most important result presented in the thesis. Calculated weighting functions showed\r\nsampling of the mesosphere over a 12 km layer centered\r\nat roughly 99 km. The doppler shifts have a signature which matches westward, horizontal winds - being strongly \"blue\" on the east/dayside limb, zero near the center and strongly \"red\" on the west/nightside limb of the planet. Smoothed wind measurements were best fitted in a least squares sense for a mean zonal flow of 132\u00b110 ms^(-1). A smaller (\u226440 ms^(-1))subsolar-to-antisolar flow may have been superimposed on the dominant zonal flow in 1988. These measurements indicate either a reversal of the mesospheric cyclostrophic breakdown inferred by Pioneer Venus or the influence of uninvestigated dynamical forces.
\r\n\r\nThe 1 MHz and 50 kHz filter bank spectra were merged to look at the entire 115 GHz CO line. These 1988 CO spectra show a decided local time dependency, becoming progressively deeper from the afternoon to the evening hours. A constrained least-squares inversion algorithm was used to solve for the local CO mixing ratio profile over local time and latitude. The resultant CO mixing ratio remains constant with height at a value of several 10^(-5) in the late afternoon hours but increases from 10^(-4) at 80 km to 10^(-3) at 100 km in the night hours. The highest CO abundances occurred after local 10 PM and centered about the equator between 40\u00b0N and 40\u00b0S. This distribution of CO abundance fulfills predictions from research based on disk-average CO spectra and photochemical models. Only the late afternoon profiles are surprising, showing essentially little CO rather than an expected moderate CO abundance from dayside photodissociation of CO_2.
\r\n", "doi": "10.7907/qkzq-0655", "publication_date": "1992", "thesis_type": "phd", "thesis_year": "1992" }, { "id": "thesis:4334", "collection": "thesis", "collection_id": "4334", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-10302008-151649", "primary_object_url": { "basename": "Grossman_aw_1990.pdf", "content": "final", "filesize": 9686525, "license": "other", "mime_type": "application/pdf", "url": "/4334/1/Grossman_aw_1990.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Microwave imaging of Saturn's deep atmosphere and rings", "author": [ { "family_name": "Grossman", "given_name": "Arie William", "clpid": "Grossman-Arie-William" } ], "thesis_advisor": [ { "family_name": "Muhleman", "given_name": "Duane Owen", "clpid": "Muhleman-D-O" } ], "thesis_committee": [ { "family_name": "Unknown", "given_name": "Unknown" } ], "local_group": [ { "literal": "Owens Valley Radio Observatory (OVRO)" }, { "literal": "div_gps" } ], "abstract": "This work presents an analysis of microwave images of Saturn's atmosphere and rings. Interferometer observations at wavelengths of 0.27, 2.01, 3.53, 6.17, and 20.13 centimeters and precise application of synthesis imaging techniques yielded brightness and polarization maps of unsurpassed resolution and sensitivity. Linear polarization is detected from the ring ansea, and brightness variations in the deep atmosphere and the rings are revealed for the first time.\r\n\r\nThe disk-integrated spectrum of Saturn is interpreted within the context of a radiative transfer model that requires the NH3 mixing ratio to take on a value of 0.9 to 1.1 x10[superscript -4] (0.5-0.6 times solar) directly below the ammonia ice cloud at a pressure of 1.4 bar. The NH[subscript 3] mixing ratio increases with depth to a value of 5.0 to 6.5 x10[superscript -4] (2.9-3.7 times solar) at a pressure of 6 bar. The variation of NH3 with depth can be entirely accounted for by the presence of 11-14 times solar abundance of H[subscript 2]S, which reacts with NH[subscript 3] to produce a substantial NH[subscript 4]SH cloud.\r\n\r\nLatitudinal variations in brightness temperature indicate that the saturated vapor abundance of ammonia decreases by 50% from equator to pole within the cloud deck. At greater depths the latitudinal variations of ammonia are consistent with alternating zones of concentration and depletion caused by vertical motions. An apparent depletion in northern mid-latitudes is well-correlated with a decrease in infrared opacity and depressed cloud top levels, indicating deep-seated downwelling.\r\n\r\nThe size, composition, and shape of particles comprising the rings of Saturn are constrained by modeling the emission, scattering, and extinction of radiation by the rings. The observations can be fit by a incremental power-law particle size distribution with exponent in the range 2.6-3.0 for the combined A and B rings, assuming a classical many-particle-thick layer. The wavelength dependence of the optical depths places a strict lower limit of 1 cm on particle sizes in the classical rings. Observations of thermal emission from the rings further constrain the mass fraction of uniformly mixed silicate impurities to be less than 1%. Azimuthal variations in brightness and linear polarization rule out the possibility that the particles are smooth, convex objects, and favor a model in which the particles are irregularly shaped.\r\n", "doi": "10.7907/svtf-j306", "publication_date": "1990", "thesis_type": "phd", "thesis_year": "1990" }, { "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: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: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: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: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:4309", "collection": "thesis", "collection_id": "4309", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-10292008-160948", "primary_object_url": { "basename": "Schloerb_fp_1978.pdf", "content": "final", "filesize": 6457901, "license": "other", "mime_type": "application/pdf", "url": "/4309/1/Schloerb_fp_1978.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Radio Interferometric Investigations of Saturn's Rings at 3.71- and 1.30-cm Wavelengths", "author": [ { "family_name": "Schloerb", "given_name": "Frederic Peter", "clpid": "Schloerb-Frederic-Peter" } ], "thesis_advisor": [ { "family_name": "Muhleman", "given_name": "Duane Owen", "clpid": "Muhleman-D-O" } ], "thesis_committee": [ { "family_name": "Unknown", "given_name": "Unknown" } ], "local_group": [ { "literal": "Owens Valley Radio Observatory (OVRO)" }, { "literal": "div_gps" } ], "abstract": "NOTE: See Abstract within Thesis for Tables of Summary Results.\r\n\r\nInterferometric observations of Saturn and the rings have been obtained at 3.71 and 1.30 cm wavelengths. The observations have been analyzed by both model fitting and aperture synthesis techniques. They show that the rings have a very low brightness temperature, but attenuate the thermal emission from the planet significantly where they cross in front of it. The latter effect, when combined with the estimate of the ring brightness temperature, permits the optical depths of the rings to be estimated. The fits of the interferometric data to Saturn models in which the A and B rings are combined into a single ring are given in Table (1). The 3.71 cm observations were made at two epochs and the relative areas of the A and B rings that obscured the planet were different. The apparently inconsistent optical depth results of the two 3.71 cm data sets, then, indicate that the A ring optical depth is significantly less than that of the B ring. The relative areas of the A and B rings are the same for the 1976 1.30 cm and 3.71 cm observations and their optical depth results may be directly compared. They indicate that the ring optical depths are the same at the two wavelengths. These optical depths are quite similar to those estimated at visible wavelengths. The ring brightness temperatures, which are shown in the table normalized by the brightness temperature of the planet to remove any errors in the absolute calibration of the data, are also the same at the two wavelengths. No variation in the brightness temperature of the rings with tilt angle (B) was detected. A significant amount of radiation from the C ring was detected by the 3.71 cm observations, and the ring was also found to attenuate the planetary emission significantly. Unfortunately, the 1.30 cm observations were not sensitive enough to detect the C ring. The brightness temperature and optical depth results for the individual rings that are implied by all of the 3.71 cm observations are given in Table (ii). Limb-darkening of the planetary emission was simulated by solving for the best fitting planetary radius. No limb-darkening was detected at 3.71 cm, but an apparently significant amount was detected at 1.30 cm. The results at the two wavelengths are significantly different and indicate that the planet is more limb-dark at 1.30 cm than at 3.71 cm. This finding is interesting since it is contrary to what was predicted by atmospheric models which fit the Saturn microwave spectrum. The aperture synthesis analysis is independent of the model fitting and can be used to confirm its results and search for new features not included in the models. The aperture synthesis maps confirm the model fitting results and require no new brightness structures. In particular, no azimuthal variations of the brightness temperature of the rings were detected. The aperture synthesis maps also indicated that the true position of Saturn may be offset from the values given in the American Ephemeris and Nautical Almanac by about 0.3 arcsec. Consideration of simple physical models of the rings has shown that the radiation from the rings at centimeter wavelengths is almost entirely thermal emission from the planet that is scattered to the Earth by the ring particles. The models indicate that the ring particles are very good scatterers and very poor emitters at microwave wavelengths, and this conclusion sets constraints upon the size and composition of the ring particles. The similarity between the optical depths of the rings at visible and centimeter wavelengths probably indicates that the particles are much larger (\u2265 1 meter) than the centimeter wavelengths. The large sizes and excellent scattering properties of the particles indicate that they are composed of either a highly reflective or transparent material. At this time water ice is the most likely candidate, since it has been detected in the rings spectroscopically and is known to be highly transparent to microwaves at the low temperatures found at Saturn's rings.
", "doi": "10.7907/ztk7-wf79", "publication_date": "1978", "thesis_type": "phd", "thesis_year": "1978" }, { "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:6530", "collection": "thesis", "collection_id": "6530", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06272011-145049521", "primary_object_url": { "basename": "Cuzzi_jn_1973.pdf", "content": "final", "filesize": 39604035, "license": "other", "mime_type": "application/pdf", "url": "/6530/1/Cuzzi_jn_1973.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "The Subsurface Nature of Mercury and Mars from Thermal Microwave Emission", "author": [ { "family_name": "Cuzzi", "given_name": "Jeffrey Nicholas", "clpid": "Cuzzi-Jeffrey-Nicholas" } ], "thesis_advisor": [ { "family_name": "Muhleman", "given_name": "Duane Owen", "clpid": "Muhleman-D-O" } ], "thesis_committee": [ { "family_name": "Unknown", "given_name": "Unknown" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "Detailed numerical modeling techniques are applied to the analysis of microwave observations of Mercury and Mars. The model calculations include the effects of orbital-axial resonance and dependence of regolith properties (e.g. specific heat and thermal conductivity) on temperature\r\nin the case of Mercury, and for the effects of seasonally varying CO_2 frost caps in the case of Mars. Variations of geocentric aspect from one observation period to the next are treated for both planets. The dielectric properties of the subsurfaces of these planets are treated as\r\nindependent of temperature and homogeneous with depth and location on the planet.\r\n\r\nObservations of Mercury were made at 3.71, 6, and 18 cm, and\r\npreviously published observations at .31, .33, and 3.75 cm are also employed in the analysis. The Mercury data appear to be consistent with the presence of a dry, porous regolith in which the radiative transport of heat is important in the total thermal conductivity. The ratio of\r\nradiative to contact thermal conductivity, \u03c7, is normally evaluated at T = 350\u00b0 K, and it is found that these data limit \u03c7 thus defined to the range 0.4 < \u03c7 < 1.0. A value for the effective subsurface dielectric constant is determined from interferometric measurements at 3.71 cm presented\r\nhere. This value (\u03b5 = 2.0 \u00b1 .16 ) is then corrected for the effects of surface roughness to yield a value for the dielectric constant of the regolith of \u03b5 = 2.4 \u00b1 .3. Final values of other parameters are:\r\n\r\ntan \u0394 = regolith loss tangent = .0075 \u00b1 .002\r\n\r\n\u03b3 = thermal inertia = .0014^(+.0021_(-.0008) cal cm ^(-2) deg ^(-1) sec ^(-\u00bd).\r\n\r\nIn a similar way, expected microwave spectra of Mars are computed using accurate aspect geometry and a thermal model that includes seasonal polar cap effects. It is found that for a range of loss tangents characteristic of dry particulate geological materials (.003 < tan \u0394 < .015), and for values of other surface parameters determined independently, the observable spectrum of Mars in the microwave region is \"flat\" from 0.1 to 21 cm to within the\r\naccuracy of the present data , and that a regolith of homogeneous, lunar-like properties is completely consistent with the existing data set when polar cap effects are considered. This result differs from that predicted by the\r\nanalytical theory in common use which is in apparent conflict with the observed spectra for values of the surface parameters similar to those found for the Moon or Mercury.\r\n\r\nFinal values of other relevant parameters are:\r\n\r\n\u03b3 = thermal inertia = .006 cal cm ^(-2) deg ^(-1) sec ^(-\u00bd)\r\n\r\n\u03b5 = regolith dielectric constant = 2 .5 \u00b1 .3\r\n\r\nA = bolometric Bond albedo = .25\r\n\r\nE = infrared emissivity = .90.\r\n", "doi": "10.7907/MBPM-GS43", "publication_date": "1973", "thesis_type": "phd", "thesis_year": "1973" } ]