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.