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Abstract: Our ground-based measurements of martian atmospheric water vapor, made throughout to 249°, 24 September 1998 to 23 November 1999, during Mars year 24 (MY 24), show changes in Mars'' humidity on hourly, daily, and seasonal timescales. We made concomitant measurement of nearby CO2 bands, and when possible, results were corrected for aerosol extinction using aerosol optical depths derived from our own CO2 analysis. Where there is spatial and temporal overlap, similar results are obtained for water vapor abundances and aerosol opacities as those observed from the Thermal Emission Spectrometer on Mars Global Surveyor. In addition some further discussion of our published earlier water vapor measurements (1991–1995) is included. Six results from this data set are: (1) the measured aerosol opacity in Mars atmosphere was variable but not greater than , with almost no clear atmosphere being observed, (2) measurements made with the slit crossing many hours of local time on Mars'' Earth-facing disk show a diurnal pattern with highest abundances at mid-day and low abundance in very early morning and late afternoon for some but not all measurements, (3) water vapor abundance is patchy on hourly and daily time scales but follows the usual seasonal trends seen by instrumentation on the Mars Atmospheric Water Detector on the Viking Orbiters and by the Thermal Emission Spectrometer on Mars Global Surveyor, (4) there is a slight longitudinal correlation with the ground-ice observed by the Gamma Ray Spectrometer on Mars Odyssey, (5) there is evidence of the Low Southern Latitude Summer Minimum in our water vapor measurements but our data set for southern summer is limited, and (6) MY 24 appears to be wetter than MY 22 and MY 23. [Copyright &y& Elsevier]

Measurements of martian atmospheric water vapor made throughout Ls = 18.0°–146.4° (October 3, 1996–July 12, 1997) show changes in Mars humidity on hourly, daily, and seasonal time scales. Because our observing program during the 1996–1997 Mars apparition did not include concomitant measurement of nearby CO2 bands, high northern latitude data were corrected for dust and aerosol extinction assuming an optical depth of 0.8, consistent with ground-based and HST imaging of northern dust storms. All other measurements with airmass greater than 3.5 were corrected using a total optical depth of 0.5. Three dominant results from this data set are as follows: (1) pre- and post-opposition measurements made with the slit crossing many hours of local time on Mars’ Earth-facing disk show a distinct diurnal pattern with highest abundances around and slightly after noon with low abundances in the late afternoon, (2) measurements of water vapor over the Mars Pathfinder landing site (Carl Sagan Memorial Station) on July 12, 1997, found 21 ppt μm in the spatial sector centered near 19° latitude, 36° longitude while abundances around the site varied from as low as 6 to as high as 28 ppt μm, and (3) water vapor abundance is patchy on hourly and daily time scales but follows the usual seasonal trends. [Copyright &y& Elsevier]