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Planetary atmospheres: probing structure through millimeterwave observations of carbon monoxide

Citation

Gurwell, Mark Andrew (1996) Planetary atmospheres: probing structure through millimeterwave observations of carbon monoxide. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/wbs1-8j46. https://resolver.caltech.edu/CaltechTHESIS:02052013-152025528

Abstract

This thesis consists of inteferometric observation of carbon monoxide from three planetary atmospheres. The observations address specific questions about the state and structure of each atmosphere. The analysis and results for each planetary body are contained within individual chapters of the thesis and the abstract for each is reproduced below.

Titan: Evidence for Well-Mixed Vertical Profile

We report on new millimeter heterodyne observations of the ^(12)CO J(1 - 0) rotational transition from the stratosphere of Titan made in October 1994 with the Owens Valley Radio Observatory Millimeter Array. The spectrum obtained clearly exhibits a strong emission core over the ~600 MHz bandwidth of the upper sideband spectrometer. The lineshape, referenced to the flat spectrum simultaneously observed in the lower sideband was inverted to determine a best fit CO mixing ratio profile consistent with the observations. The bet fit profile is a constant mixing ratio of 5 ± 1 x 10^(-5) over the altitude range of 60- 200 km. Combined with IR observation of tropospheric CO (ƒco = 6 x 10^(-5), Lutz et al. 1983) this provides strong evidence that CO is well mixed from the surface to at least 200 km in Titan’s atmosphere.

Mars: Thermal Structure from 0-70 km

Millimeter-wave heterodyne observations of the ^(12)CO J (l - 0) rotational transition from the atmosphere of Mars were made on three dates in February 1993 with the Owens Valley Radio Observatory Millimeter Array. These observations yielded high-quality spectra with a spatial resolution of 4.2" on a 12.5" diameter Mars. The spectra were numerically inverted for profiles of the local atmospheric temperature from 0 to 70 km, assuming a constant CO mixing ratio for the atmosphere. The derived average low latitude atmospheric temperature profile is approximately 20 K cooler than reference temperature profiles compiled during the Viking era. This new temperature profile is well-matched by cooler profiles determined from whole disk CO measurements, suggesting very little dust loading of the atmosphere at the time of the observations (Clancy et al. 1990). In addition, the revealed thermal structure shows variation with latitude, and these temperature profiles compare well with profiles derived from Mariner 9 IRIS observations (Leovy 1982, Santee and Crisp 1993) and calculated thermal structure from the Mars General Circulation Model (Haberle et al.. 1993). The temperature profiles were averaged in local time and the resulting cross-section of temperature as a function of pressure and latitude used to infer the mean zonal circulation of the atmosphere. These wind results are somewhat compromised by the relatively low spatial resolution of the observation but do qualitatively match both inferred zonal winds from the Mariner 9 IRIS observations and Mars GCM calculations. These initial observations point toward the desirability of further interferometric measurements.

Venus: Temporal Variations of the Mesophere

Millimeter-wave heterodyne observations of the ^(12)CO J(1-0) rotational transition from the mesosphere of Venus were made in early November and early December 1994 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 spectra were numerically inverted for profiles of the local CO mixing ratio from 80 to 105 km, assuming a Pioneer Venus mean temperature profile for the atmosphere. For each day the revealed CO distribution shows a nightside maximum centered at low latitudes and shifted from the anti-solar point toward the morning terminator. Both clays show a clear latitudinal falloff in the CO abundance. In November the maximum was centered at roughly 2^h local time at 100 km, while in December the maximum was at roughly 4 – 4.5^h local time at 100 km. In addition, CO abundances were slightly higher in November. The changes in the CO distribution are examined in the context of the mesospheric circulation model of Clancy and Muhleman (1985b). The increased shift away from the anti-solar point and decreased CO abundance for the December observations both point toward increased zonal and/or decreased sub-solar to anti-solar circulation within the mesosphere during the month between observations.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Planetary Science and Astronomy
Degree Grantor:California Institute of Technology
Division:Geological and Planetary Sciences
Major Option:Planetary Sciences
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Muhleman, Duane Owen
Thesis Committee:
  • Unknown, Unknown
Defense Date:21 July 1995
Record Number:CaltechTHESIS:02052013-152025528
Persistent URL:https://resolver.caltech.edu/CaltechTHESIS:02052013-152025528
DOI:10.7907/wbs1-8j46
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:7464
Collection:CaltechTHESIS
Deposited By: John Wade
Deposited On:06 Feb 2013 00:01
Last Modified:19 Apr 2021 22:37

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