Other
Scientific paper
Sep 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008dps....40.0608k&link_type=abstract
American Astronomical Society, DPS meeting #40, #6.08; Bulletin of the American Astronomical Society, Vol. 40, p.397
Other
Scientific paper
We have flown a series of accelerometer experiments aboard 3 satellites orbiting Mars: Mars Reconnaissance Orbiter (MRO), Mars Odyssey (MO), and Mars Global Surveyor (MGS). From these measurements we have obtained atmospheric densities from atmospheric drag, and scale heights and temperatures from vertical structure of drag effects. The orbits precess resulting in changes in the latitude of measurement and the generation of densities from pole to pole on the day and nightside. Measurements are obtained from 100km to near 200km. Large differences occur between perihelion and aphelion and due to the 11-year solar activity cycle. Intermediate sized dust storms can increase densities by a factor of 3, which can potentially endanger spacecraft missions. However, to date no missions have been lost due to drag effects.
One of our major discoveries has been the detection of winter polar warming. The phenomenon may be caused by meridional transport from the summer to winter hemisphere and sinking near the winter pole producing strong adiabatic heating resulting in a rise of temperatures of nearly 100K.
Temperatures within 40° latitude of the equator remain fairly constant. On the nightside near 3AM when temperatures should reach a minimum we find exospheric temperatures of about 130K. Temperatures rise up to about 160km and then asymptotically approach the exospheric temperature. These nightside temperatures are close to the MTGCM theoretical model of Bougher et al.
However, on the dayside we find exospheric temperatures rising to near 200K in the afternoon, during low solar activity. These are cooler temperatures than predicted in the MTGCM theoretical model of Bougher et al. This may result in less planetary escape than expected of H2O and other species altering the long-term climatology of the Mars atmosphere.
These studies provide the most detailed determination of the global properties of the upper atmosphere.
Bougher Stephen
Keating Gerald M.
Theriot Michael
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