No abstract

No abstract

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/zm)) 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 L, 320-340) to 36.4 pr/zm (L, 100) at high northern latitudes. Strong latitude variations were observed for all L, sea. sons, with la. te spring and summers wet in both hemispheres. Northern latitudes are up to 5 times wetter than southern latitudes. Equatorial regions (30øS-30øN) show a rather stable abundance of atmospheric water varying between 2 and 20 pr/zm, while much larger variations are observed at high latitudes. Southern atmospheric water drops below 10 pr/zm 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. Jr. At opposition, 90 ø of Martian longitude (~14.6ø/h) rotates beneath our spectrograph slit during one long observing night. Because we take multiple 15-min images throughout an observing night, we have zonal resolution within a larger data set than is analyzed here. This paper does not address zonal variations because we wished to focus our attention on the latitude and seasonal variations along the central meridian of the Earth-facing disk of Mars. Zonal comparisons will be explored in detail in future publications. 23,229 23,230 SPRAGUE ET AL.: MARTIAN WATER VAPOR, 1988-1995

No abstract

No abstract