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D. M. Kass, A. P. Ingersoll (Caltech), J. C. Pearl (NASA/GSFC), R. M. Haberle (NASA/Ames Research Center), TES Team
We have successfully assimilated TES (Thermal Emission Spectrometer) atmospheric profiles into the Ames Mars GCM (General Circulation Model---Haberle {\it et al.}, {\sl JGR, \bf 98}, 3093-3123, 1993). We are using steady-state Kalman filtering (Banfield {\it et al.}, {\sl J. Atmos. Sci., \bf 52}, 737-753, 1995) modified to handle the irregular and unusual observing pattern dictated by the elliptical orbit during aerobraking. We have assimilated 25 sols (Martian days) of data in Northern Fall (L\rm s ~ 198 to 214---orbits 20 through 36). We also hope to assimilate data from before and during the Noachis dust storm (L\rm s ~ 224).
The first goal of the assimilation is to predict the global fields for the dynamical variables (P,T,U and V) based on the limited sampling of a single spacecraft. This allows us to use the sparse (in time and space) sampling to look at global issues. The second goal is to improve our understanding of the climatology of Mars. By combining the data, we can remove the weather and obtain a climatological mean for this season. This can then be used for comparison to models of the Martian atmosphere. If possible, we hope to search for unusual weather that might have initiated the Noachis dust storm.
Unfortunately, the highly elliptical orbit and resulting observing pattern are not conductive to data assimilation. The major dynamical variability at this season is in the Northern hemisphere which is poorly sampled by the data. Despite the problem, the assimilation is able to make significant changes to the GCM model. Notably, it affects the phasing of the northern storm belt. In this way, the Mars GCM is creating {\it this} Martian Fall and not a random Martian Fall.