A comparison of MGS Phase 1 aerobraking radio occultation data and the NASA Ames Mars GCM

The NASA Ames Mars general circulation model (MGCM) is used to investigate how different phenomena in the Martian climate system combine to produce te mperature profiles measured by the Radioscience Instrument (RS) aboard Mars Global Surveyor (MGS) in early 1998. When integrated with dust amounts con sistent with Thermal Emission Spectrometer (TES) observations, and with a t opography data set determined from the Mars Orbiting Laser Altimeter (MOLA) , modeled temperature profiles are within 5-10 EC of observations. Modeled and measured pro-files in the winter subtropics are warmer than pure radiat ive-convective considerations suggest, providing further evidence of strong dynamical warming associated with descent in the Hadley cell. South of 40 degrees S, the best fit to the data is obtained by confining airborne dust to below 2 scale heights in this region. The differences in the strength of low-level inversions found in the MGCM and in the RS data indicate the pre sence of either a low-level radiative cooling mechanism such as isolated du st clouds or water-ice clouds, or a dynamical mechanism such as low-level g ravity wave drag. When initialized with a mean surface pressure that gives the best fit to Viking lander measurements, the model matches RS surface pr essure data to within 0.1 mbar. This consistency is a further validation of the MGCM and shows how GCMs can be used to interpret measurements of surfa ce pressure taken at different locations using different methods.