Water Vapor Map Of Mars Near Summer Solstice Using Ground-Based Infrared Spectroscopy
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Ground-based spatial mapping of Mars provides a unique way to retrieve the global distribution of minor atmospheric species and to study transient phenomena or possible variations with the local hour. We have obtained an instantaneous map of water vapor on Mars near summer solstice (Ls = 80 degrees) using the Texas Echelon Cross Echelle Spectrograph (TEXES) at the NASA Infrared Telescope Facility (IRTF) at Mauna Kea Observatory. Data have been obtained in the 1230-1245 cm(-1) range (lambda = 8.1 mu m), with a spatial resolution of 1.1 arcsec (after convolution) and a spectral resolution of 0.012 cm(-1) (R = 10(5)). The map has been retrieved from the line depth of a weak HDO transition, compared with the line depth of a weak CO(2) nearby transition. The TEXES map exhibits a strong maximum around the northern pole, as expected from previous observations and from climate model predictions. More interestingly, it shows longitudinal variations, both at high northern latitudes and at mid-latitudes, in close agreement with the predictions of the Global Climate Model developed at the Laboratoire de Meteorologie Dynamique (LMD GCM). The inferred water vapor mixing ratio is also in good agreement with the model predictions. The longitudinal variations at mid latitudes show a general enhancement toward the east. They do not seem to be due to the effect of local hour, but can be explained by dynamical effects generated by the topography. The map of surface temperatures, inferred from the continuum flux, is surprisingly different from the map expected from the climate models; the source of this discrepancy is still unclear.