The Oscillatory State of the Mars Climate: 1997 Microwave Observations

R.T. Clancy (Space Science Institute), B.J. Sandor (JPL)

Temperature profiling of the Mars atmosphere in 1996-1997 indicates a very cold, dust-free global atmosphere in which water vapor is saturating at very low altitudes. Globally extended water ice clouds are seen in HST imaging at this time. Such behavior is in fact typical of the conditions observed for Mars northern spring/summer (around aphelion) for the past four Mars years. There are, however, several new apsects to the 1996-1997 observations. Higher frequency observations (346 GHz) from the James Clerk Maxwell Telescope on Mauna Kea provide atmospheric temperature measurements up to the 5 microbar pressure level (or roughly 70-75 km altitude). Such measurements in Sept96 (Ls=8) reveal atmospheric temperatures falling below 120K, or near the saturation temperature for CO2 at these altitudes. In addition, we have observed global 20K temperature fluctuations in the lower scale height (10 km) of the Mars atmosphere, most notably around March 10 (Ls=90). We associate this lower atmospheric heating with northern summer dust storm activity, which is also identified from HST imaging. Furhermore, we argue that the rapid decay timescale observed for dust heating (4 days) is a strong indicator of critical dust/ice aerosol interactions in the Mars climate system.