General circulation model simulations of the Mars Pathfinder atmospheric structure investigation/meteorology data

The NASA Ames Mars General Circulation Model is used to interpret selected results from the Mars Pathfinder atmospheric structure instrument/meteorolo gy (ASI/MET) experiment. The present version of the model has an improved s oil thermal model, a new boundary layer scheme, and a correction for non-lo cal thermodynamic equilibrium effects at solar wavelengths. We find good ag reement with the ASI/MET entry data if the dust observed at the Pathfinder site is assumed to be distributed throughout the lowest five to six scale h eights. This implies that the dust is globally distributed as well. In the lower atmosphere the inversion between 10 and 16 km in Pathfinder's entry p rofile is likely due to thermal emission from a water ice cloud in that reg ion. In the upper atmosphere (above 50 km), dynamical processes, tides in p articular, appear to have a cooling effect and may play an important role i n driving temperatures toward the CO2 condensation temperature near 80 km. Near-surface air temperatures and wind directions are well simulated by the model by assuming a low surface albedo (0.16) and moderately high soil the rmal inertia (336 SI). However, modeled tidal surface pressure amplitudes a re about a factor of 2 smaller than observed. This may indicate that the mo del is not properly simulating interference effects between eastward and we stward modes.