Mars nighttime water-ice clouds

The Mars Global Surveyor (MGS) Thermal Emission Spectrometer (TES) nighttime (2 am) data are underutilized due to the presence of the radiometric error that precludes the use of the ';standard' retrieval algorithm. We have developed a technique that corrects for radiometric error and enables retrievals of atmospheric aerosols opacities at night. We do not detect any diurnal variability in dust abundances within the uncertainty of the retrieval (which is relatively large). Nighttime water ice clouds reach their maximum areal extent and highest opacities during the aphelion season, similar to the daytime clouds. During this time extensive clouds are found over and around the Tharsis volcanoes, Olympus Mons, western Valles Marineris, and between Syrtis Major and Elysium Planitia. Perihelion season is characterized by the thinner nighttime clouds appearing south of the Tharsis and over western Valles Marineris and north of the Hellas basin. The seasonal spatial patterns of the nighttime water ice clouds are highly repeatable year over year.