Physics
Scientific paper
Dec 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003agufm.p21c..05b&link_type=abstract
American Geophysical Union, Fall Meeting 2003, abstract #P21C-05
Physics
0343 Planetary Atmospheres (5405, 5407, 5409, 5704, 5705, 5707), 0358 Thermosphere: Energy Deposition, 3369 Thermospheric Dynamics (0358), 6225 Mars
Scientific paper
New Mars thermospheric density (and inferred scale height and temperature) information was obtained by the Mars Odyssey Accelerometer during aerobraking exercises (Ls = 265-310; F10.7 = 175-200) covering Northern latitudes on both the dayside and nightside of the planet. Altogether, 600 vertical structures were obtained over 95 to nearly 170 km during this perihelion season on Mars. No global or regional dust storms erupted during this Odyssey aerobraking period (Sept. 2001 to Jan. 2002). Also, there was apparently no substantial effect of the dust storm that occurred well before the start of Odyssey aerobraking (summer 2001). Odyssey provided the first in-situ determinations of atmospheric density at Northern latitudes during winter, extending to nearly the equator (on the nightside) as aerobrakling concluded. Only preliminary analysis of Odyssey aerobraking data over 100-130 km has thusfar been conducted [Keating et al., 2003]. Densities into the Northern polar night appear to decrease as expected from previous MGS Phase 1 Accelerometer data obtained during the same season (at lower latitudes). However, the Northern winter night revealed by Odyssey possessed a distinct polar warming (over 100-130 km) that intensified as the spacecraft periapsis approached the pole. Temperatures near 100-110 km were discovered to increase with latitude (60-90N) from 100 to 200 K, maximizing near the North pole on the Mars nightside. This winter polar warming may be generated from adiabatic heating resulting from the subsiding branch of a strong inter-hemispheric circulation cell (South to North) during perihelion [Forget et al., 1999]. No such winter polar warming was observed during MGS Phase 2 (MGS2) aerobraking exercises over the Southern polar night during aphelion conditions (Ls = 90). It is likely that variable seasonal dust distributions contribute to a stronger summer-to-winter circulation cell supplying dynamical heating to the Northern winter pole (Ls = 270); the opposite summer-to-winter circulation cell (Ls = 90) is weaker resulting in reduced dynamical heating to the Southern winter polar region. The coupled NASA Ames Mars General Circulation Model (MGCM) and the Michigan Mars Thermospheric General Circulation Model (MTGCM) are exercised for both perihelion and aphelion conditions using observed MGS Thermal Emission Spectrometer (TES) dust distributions appropriate to the Odyssey and MGS2 aerobraking periods. Improved CO2 15-micron cooling and near IR heating formulations are used in both MGCM and MTGCM codes resulting in upgraded simulations for this study. Latitudinal distributions of densities and temperatures are presented from these coupled simulations and contrasted with longitudinally averaged aerobraking data. The underlying MTGCM heating terms are displayed in order to illustrate the seasonally variable processes that contribute to polar warming in the Mars thermosphere.
Bougher Stephen W.
Murphy Ronald J.
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