DPS Meeting, Madison, October 1998
Session 11P. Mars Atmosphere I, II, III, IV
Contributed Poster Session, Monday, October 12, 1998, 4:10-5:30pm, Hall of Ideas

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[11P.09] Martian Atmospheric Water Vapor: The 1996-1998 Apparition

E. S. Barker (McDonald Obs., Univ. of Texas at Austin)

Between October 1996 and November 1997, seasonal coverage of Martian water vapor in Ls concentrated on the northern spring summer season with samples at Ls = 25\circ, 46\circ, 67\circ, 74\circ, 83\circ before Mars' opposition; and on the northern late-summer, early-fall season at Ls = 132\circ, 143\circ, 166\circ, 181\circ, 212\circ after opposition. The slit was placed either in the N-S direction along the central meridian to study the latitudinal distribution or E-W to study the diurnal behavior. High-dispersion, CCD echelle spectra yielded 87 continuous H2O vapor profiles across the Martian disk.

To improve the inter-comparability of ground-based datasets (Arizona, Texas), we are using: (1) HITRAN96 line strengths for the (211) band of H2O which are 20-40% stronger (depending on the line and effective temperature) than those used previously; and (2) the Mars GCM (Haberle, personal communication) to predict the effective atmospheric temperature for each Ls and sampled Martian latitude and longitude. Evidence for the following summary conclusions will be presented.\\ \bullet\hspace {1mm}Spatial variations of 4x or greater are present at all sampled seasons.\\ \bullet\hspace {1mm}During the northern spring season, the latitude region containing the maximum amount of water vapor moves northward as the season progress, but the maximum is at least 30\circ north of sub-solar latitude.\\ \bullet\hspace {1mm}During the pre-opposition period (Ls = 25\circ to 83\circ), nominal amounts of Martian water vapor were observed, increasing to maximum amounts of (20 to 25\mum of ppt. H2O) at higher northern latitudes (55\circ to 75\circ).\\ \bullet\hspace {1mm}Barely detectable 1-3\mum amounts were measured during these seasons at all southern latitudes (0\circ to -30\circ).\\ \bullet\hspace {1mm}Measurements of the diurnal change at different Martian latitudes showed quite low abundances (2-5\mum) above both the morning and evening terminator regions with a maximum about 1 hour after local noon.\\ \bullet\hspace {1mm}Ground-based measurements showed 10.5±1.5\mum of ppt. H2O above the Pathfinder site on July 5, 1997.\\ Research supported by NASA grant NAG5-6140.

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