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J.R. Murphy (New Mexico State University), T.Z. Martin (Jet Propulsion Laboratory)
Longitudinal structure in the 90-120 km martian atmospheric density field has been detected by both the Mars Global Surveyor and Mars Odyssey orbiters during their mission-initiating aerobraking phases. This longitudinal pattern has been demonstrated to result from the presence of so-called ‘non-migrating’ thermal tidal waves present at those altitudes (Wilson, GRL, 2002). These same waves have been both directly (during aerobraking) and indirectly (during mapping) diagnosed in lower (10-40 km) atmospheric temperatures derived from MGS Thermal Emission Spectrometer (TES) spectra (Wilson, GRL, 2000; Banfield et al., JGR-P, 2000;2003). The Mars Horizon Sensor Assembly (MHSA) engineering instrument onboard MGS provided an additional capability of deriving ~25 km level atmospheric temperatures, and did so at 6 local times of sol compared to TES’ two local times of sol. This enhanced MHSA temporal coverage enables direct determination of amplitudes and phases of several important migrating and non-migrating tidal components during MGS mapping. Numerical model results obtained with the NASA Ames Mars GCM, from simulations forced with the spatial and temporal pattern of suspended dust opacity (derived from TES spectra), indicate realistic model-generated tidal fields when compared to MHSA analysis results. Though complete MHSA data are available only through August 2001 (~Ls 230 of MGS mapping year 2), comparison of the numerically modeled atmospheric tidal response during late 2001 with the Mars Odyssey aerobraking density measurements at that same time permits for a correlation between the lower atmosphere tidal field and the contemporaneous upper atmosphere manifestation of these same tidal components. This correlation will illustrate the vertical propagation characteristics of these waves and will also provide some guidance in attempting to predict the magnitude of aerobraking altitude density variations based upon derived lower atmosphere temperature fields. This work is supported by NASA’s Planetary Atmospheres Program (NAG5-12123) and Mars Data Analysis Program/Jet Propulsion Lab (JPL/1225584).
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Bulletin of the American Astronomical Society, 36 #4
© 2004. The American Astronomical Soceity.