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D. P. Hinson, G. L. Tyler (Stanford Univ.), F. M. Flasar (GSFC), R. Woo (JPL), R. A. Simpson, J. D. Twicken (Stanford Univ.)
More than 100 radio occultation experiments were conducted with Mars Global Surveyor in early 1998. High quality data were obtained between 28 January and 17 April, during the first half of summer in the southern hemisphere (Ls=264--313\deg). The measurements cover latitudes from 30\degN to 65\degS, solar zenith angles from 86\deg to 106\deg, and local times from 6 pm through midnight to 6 am. Profiles of the neutral atmosphere (temperature and pressure vs radius) extend from the surface to the 10 Pa pressure level. The uncertainty in the pressure measurements is smaller than the quantization of the Viking Lander data (8 Pa). The pressure data exhibit temporal variations due to seasonal condensation of the north polar cap as well as meridional gradients associated with geostrophic balance of the zonal winds. Temperature profiles are characterized by large diurnal variations within the near-surface boundary layer, meridional gradients but otherwise repetitious structure in the southern (summer) hemisphere, with deep inversions and distinct wave-like variations in the northern (winter) hemisphere. These data are also being used to determine the shape of Mars and the structure of the ionosphere near the terminator.