IRIS Mariner 9 data revisited: water and dust daily cycles

IRIS Mariner 9 data have been studied, after correction for an instrumental effect, as a function of season and local time, searching for a relation between water content of the atmosphere and dust. After averaging data for different local time bins, the vertical temperature profile and atmospheric dust content were retrieved. The temperature profile was then used for evaluation of water mixing ratio. This last procedure was without ambiguity only when no thermal inversion was found in the vertical profile. This fact limits our basic results only on the day side. Our results indicate that the ground temperature and the atmospheric temperature (mainly in the low altitudes) show a strong modulation during the day, with a peak temperature around 12-14 local time. Together with the temperature, the atmospheric water content shows a strong modulation: the peak of the water content, around 140 ppm, is observed with the peak of the temperature. The integrated atmospheric dust opacity computed at 1000 cm(-1) shows an anti-correlated behavior: peaks are observed at early morning and late evening, while a local minimum is observed around noon. Our observations, with the integrated dust opacity decreasing around noon, are consistent with a model in which a large part of atmospheric water vapor is adsorbed by dust and soil, and is released as water vapor during the hot hours. In the afternoon, water is adsorbed quickly again as new dust is added by dust devils. The vertical temperature profile does not allow, during the entire day, ice condensation around dust. The water lines and the continuum around 200-400 cm(-1) give spectral evidence of frost on soil only very early in the morning or very late in the evening. The 200-400 cm(-1) region is a very good indicator of the presence of frost. (C) 2001 Elsevier Science Ltd. All rights reserved.