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withers

HR: 16:30h
AN: P32E-12 INVITED
TI: The Upper Atmospheric Wave Structure of Mars as Determined by Mars Global Surveyor
AU: * Bougher, S W
EM: sbougher@lpl.arizona.edu
AF: Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721 United States
AU: Keating, G M
AF: George Washington University George Washington University, NASA Langley Research Center, Hampton, VA 23606 United States
AU: Forbes, J M
AF: Dept. of Aerospace Engineering Sciences, University of Colorado, Boulder, CO 80309 United States
AU: Murphy, J R
AF: Dept. of Astronomy, New Mexico State University, Las Cruces, NM 88003 United States
AU: Hollingsworth, J L
AF: NASA Ames Research Center, SJSUF, MS 245-3, Moffett Field, CA 94035 United States
AU: Wilson, R J
AF: Geophysical Fluid Dynamics Laboratory/NOAA, Princeton University, Princeton, NJ 08542 United States
AU: Withers, P G
AF: Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721 United States
AB: The best coverage of the Mars upper atmoshere available to date was obtained during recent Mars Global Surveyor (MGS) aerobraking exercises. Measurements from the MGS z-axis accelerometer (ACC) aboard MGS have provided more than 1200 vertical structures of the Mars thermospheric density and derived temperature and pressure [Keating et al. 1998; 2001]. These data have been obtained over two distinct Mars seasons : (Phase 1) approaching perihelion (Ls = 180 to 300), and (Phase 2) near aphelion (Ls = 30 to 95). The ubiquitous presence of planetary scale waves that appear fixed in longitude at lower thermospheric altitudes (90-150 km) was unexpected. Throughout both Phase 1 and 2 of aerobraking, the dominance of wave-2 and 3 features throughout low-to-mid-latitudes is evident, while wave-3 features seem to prevail in the mass density and electron density data at high Northern latitudes [Keating et al. 2000; Withers et al. 2000; Forbes and Hagan, 2000; Wilson, 2000; Bougher et al. 2001]. The diurnal coverage of the ACC data (day-night variations) is rather poor, limited to day-night data at the end of Phase 2 aerobraking. Recent data-model comparisons show that the observed density variations can be identified as eastward propagating non-migrating thermal tides with large vertical wavelengths. Mars General Circulation Model (MGCM), Mars Thermospheric General Circulation Model (MTGCM), and Mars Global Scale Wave Model (MGSWM) simulations have been performed. The general indication is that the simulated wave-2 variation is dominated by a diurnal period, wave-1 Kelvin mode (DK1) which is principally forced by the modulation of the migrating diurnal tide by wave-2 Mars topography. This interpretation is consistent with the observed phase reversal between day and night side wave-2 components. The principal components of the simulated zonal wave-3 structure are a diurnal period wave-2 Kelvin mode (DK2) and a wave-1 semidiurnal tide (SW1). The characterization of these waves is important for understanding Mars dynamics and for developing effective aerobraking strategies.
DE: 5409 Atmospheres--structure and dynamics
DE: 5445 Meteorology (3346)
DE: 6225 Mars
SC: P
MN: 2001 AGU Fall Meeting