Other
Scientific paper
Apr 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003eaeja.....1542b&link_type=abstract
EGS - AGU - EUG Joint Assembly, Abstracts from the meeting held in Nice, France, 6 - 11 April 2003, abstract #1542
Other
Scientific paper
The comparative approach to planetary problems is becoming increasingly fruitful as new information from various planet atmospheres is assimilated. In particular, Earth, Venus and Mars upper atmosphere observations and modeling studies over the past 35-years provide a useful platform for addressing similar processes in other planetary environments. It is well known from thermospheric studies that light species (e.g. H, He) are efficiently redistributed about Venus and Earth by the global scale thermospheric circulation patterns that prevail. These observed helium distributions in fact can be used as a first order tracer of the seasonal thermospheric wind patterns on these two planets. For Earth, large winter bulges of helium are observed by satellite drag and mass spectrometer data (Keating and Prior, 1968; Reber et al., 1968; Mayr et. al., 1978). For Venus (a slow retrograde rotating planet), a helium bulge is observed on the nightside, consistent with a combined subsolar- to-antisolar plus retrograde superrotating zonal flow (e.g. Niemann et al.. 1980; Bougher et al., 1997). Likewise, we anticipate that helium will serve as first order tracer of the Mars thermospheric circulation. We present new Mars Thermospheric General Circulation Model (MTGCM) simulations that provide predictions of the expected helium distribution in the Mars upper atmosphere over 100 to 300 km. A winter polar helium bulge is anticipated which could dominate total densities above about 300 km. This seasonal feature could impact spacecraft drag if orbits pass through the winter polar night region (e.g. Mars Reconnaissance Orbiter). Data are needed to confirm these MTGCM predictions and measure the global scale wind patterns at Mars. The impact of exospheric return flow upon the Mars helium distribution remains to be estimated.
Bougher Stephen
Roble Ray
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