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

Citation

Ivanov, Anton Borisovich (2000) 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. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/9mv8-hz72. https://resolver.caltech.edu/CaltechTHESIS:01302013-163300566

Abstract

The spacecraft exploration of the planet Mars in the last two decades provided scientists with an enormously rich data base. This work presents some aspects of the Mars Orbiter Laser Altimeter investigation related to the issues in the Martian climatology. The instrument continues to function on board of the Mars Global Surveyor Spacecraft.

The polar ice caps on Mars are the largest reservoirs of water on the planet. Their formation and evolution are not understood very well at this point. Ice flow, sublimation and wind erosion are believed to be the most important processes that shape the caps. We have developed a model to understand the role of sublimation for the formation of the ice caps and attempted to constrain the time scale for the formation of the observed ice caps. The model has been justified using the precise topography of the ice caps and the layered terrains that have been measured by the MOLA instrument. We argue that sublimation is a very important process for the formation of the caps, especially on the time scales greater than 10 million years.

We report the direct observations of CO_2 clouds, forming during the polar winter times over both poles. These clouds are similar over both poles and possibly represent a CO_2 snowfall. On the basis of the reflective properties and spatial occurrence, we can distinguish two major classes of clouds. We will discuss some hypotheses on the mechanisms of their formation.

Total atmospheric opacity of the Martian atmosphere at 1µm can be derived from the MOLA reflectivity measurement. Opacity estimates for the period from L_S = 105° to L_S = 220° are found to be consistent with the Viking Lander and Pathfinder values. Opacity measured in the polar regions displays storms and polar hood activity. Aerosol scale heights can be inferred from the opacity changes on some large scale topographic features. Dust scale heights are found to be lower than the atmospheric scale height. Water ice cloud scale heights are found to be consistent with the atmospheric scale height. Comparison of the MOLA derived opacity with the TES derived opacity yields information on the aerosol particle size distribution. We discuss an algorithm to derive 1µm normal albedo of the surface. 9µm dust opacity from the Thermal Emission Spectrometer (TES) is employed to remove an atmospheric attenuation from the MOLA reflectivity measurements. We will present some initial results on the calculation of the surface albedo.

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