A.L. Sprague, D.M. Hunten, R.E. Hill, B. Rizk, and W.K. Wells
Lunar and Planetary Laboratory
University of Arizona, Tucson, AZ 85721
fax 520-621-4933


(JGR, V.101,No.E10, P.23,229-23,241, Oct. 25, 1996.)

We report new measurements of Martian atmospheric water vapor for the period 1991-1995 and discuss implications of these and earlier measurements from 1988 to 1989. Our measurements indicate abundances (precipitable micrometers (pr \mic)) that show some departures from those of the 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 to the next. However, the seasonal shifts and variations between hemispheres show the same trends as observed by MAWD. Column abundances of water vapor varied from barely detectable, < 1 (at Ls 320-340) to 6.4 pr \mic \ (Ls 100) at high northern latitudes. Strong latitude variations were observed for all \lss seasons, with late spring and summers wet in both hemispheres. Northern latitudes are up to 5 times wetter than southern latitudes. Equatorial regions (30 deg. S-30 deg. N) show a rather stable abundance of atmospheric water varying between 2 and 20 pr \mic, while much larger variations are observed at high latitudes. Southern atmospheric water drops below 10 pr \mic \ rapidly in early autumn and is below our measurement threshold by late autumn. Strong diurnal variations show lowest water column abundance near the evening terminator.