Other
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufm.p31d..08k&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #P31D-08
Other
0343 Planetary Atmospheres (5210, 5405, 5704), 0350 Pressure, Density, And Temperature, 3369 Thermospheric Dynamics (0358), 5405 Atmospheres (0343, 1060), 6225 Mars
Scientific paper
The 2006 Mars Reconnaissance Orbiter (MRO) Accelerometer Experiment measurements above 100km give neutral densities and inferred temperatures over the entire Southern Hemisphere of Mars due to the precession of periapsis. When combined with our previous accelerometers on Mars Global Surveyor (MGS) and Mars Odyssey (MO), measurements are obtained showing global dynamical effects. We have discovered high amplitude (+-30 percent) planetary scale waves from all 3 spacecraft. These waves were observed from near sun-synchronous orbits and thus the observed wave 2 was apparently actually a wave 1 (non-migrating) diurnal Kelvin wave moving to the east around the planet in one Martian day (non-migrating tides) while the sun was moving (migrating) to the west around the planet in one Martian day. Thus, the wave 2 was actually a wave 1. This phenomenon occurred from the equator to near the pole. The observed phase of the wave changes from day to night by about 90 deg in longitude in accord with predictions of Forbes et al., 2002. The diurnal Kelvin wave apparently propagates upwards linking together the upper and lower atmosphere. Near the North Winter pole at 100km we discovered temperatures sharply increased with latitude from 75 deg N to 87 deg N by 85 K contrary to an atmosphere in radiative equilibrium. Apparently dynamical effects cause the phenomenon (Keating et al., 2002; Keating et al., 2002a). We proposed that perhaps there is meridional flow from the summer to winter hemisphere and then subsidence near the winter pole resulting in strong adiabatic heating near 100km (Keating et al., 2002). The Mars Thermosphere General Circulation Model (MTGCM) (Bougher et al., 2006) is consistent with our explanation. We find the winter polar warming is stronger near perihelion than near aphelion. This may be related to the stronger solar heating near perihelion. To confirm the various dynamical effects, observations are compared with the MTGCM and other GCMs. These temperature changes result in changes in density which, in turn, could produce strong aerodynamic heating endangering spacecraft. Knowledge of the nature of the thermospheric variations should reduce the risk on spacecraft from aerobraking and aerocapture.
Bougher Stephen W.
Forbes Jeffrey M.
Keating Gerald M.
Theriot M. E.
Tolson Robert H.
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