MARTIAN WATER-VAPOR, 1988-1995

We report new measurements of Martian atmospheric water vapor for the period 1991-1995 and discuss implications of these and earlier measure ments from 1988 to 1989. Our measurements indicate abundances (precipi table micrometers (pr mu m)) that show some departures from those of t he Viking Mars atmospheric water detector (MAWD) experiment and other ground-based measurement programs. Variation of water abundance within Martian season is sometimes as large as a factor of 3 from one year t o the next. However, the seasonal shifts and variations between hemisp heres show the same trends as observed by MAWD. Column abundances of w ater vapor varied from barely detectable, <1 (at L(s) 320-340) to 36.4 pr mu m (L(s) 100) at high northern latitudes. Strong latitude variat ions were observed for all L(s) seasons, with late spring and summers wet in both hemispheres. Northern latitudes are up to 5 times wetter t han southern latitudes. Equatorial regions (30 degrees S-30 degrees N) show a rather stable abundance of atmospheric water varying between 2 and 20 pr mu m, while much larger variations are observed at high lat itudes. Southern atmospheric water drops below 10 pr mu m rapidly in e arly autumn and is below our measurement threshold by late autumn. Str ong diurnal variations show lowest water column abundance near the eve ning terminator.