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We present column abundances of water vapor in Mars' atmosphere over high north latitudes for L s 46°–146° during 1996–1997 and L s 34°–180° during 1998–1999. These abundances have been obtained by ground-based high-resolving-power spectroscopy in the very near IR (8174–8200 A) from the 1.5-m Catalina observatory near Tucson, AZ. All of the measurements have been corrected for atmospheric dust opacity, which increases the measured water vapor abundance over the “apparent measurement” by appreciable amounts at long path lengths. Dust measurements in 1998–1999 were made by near simultaneous measurements, with the same instrument, of the CO 2 absorption lines in the nearby spectral region between 8689 and 8692 A. We use a doubling and adding radiative transfer code to obtain the dust optical thickness. High northern latitude dust opacities were between 0.8 and 1.0 in this data set for 1998–1999. For the high-latitude measurements made in 1996–1997 during and following observed spring dust storm activity, the dust opacity (τ dust =0.8) was adopted. The computations account for the geometry of the observations (incoming airmass, outgoing airmass, and phase angle). Measurements show a strong increase in water vapor abundance from 8 to 76 ppt. μm with onset of spring and early summer ( L s 34°–118°) followed by an abrupt drop to less than 1 ppt. μm by summer's end. |
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