HR: 0830h
AN: P41A-10
TI: MGS Accelerometer-derived profiles of Upper Atmospheric Pressures and Temperatures: Similarities,
Differences, and Winds
AU: * Withers, P
EM: withers@lpl.arizona.edu
AF: University of Arizona, Lunar and Planetary Laboratory
1629 East University Blvd, Tucson, AZ 85721
United States
AU: Bougher, S W
EM: sbougher@lpl.arizona.edu
AF: University of Arizona, Lunar and Planetary Laboratory
1629 East University Blvd, Tucson, AZ 85721
United States
AU: Keating, G M
EM: G.M.KEATING@LaRC.NASA.GOV
AF: George Washington University, NASA Langley, MS 269, Hampton, VA 23681
United States
AB:
We have used the MGS accelerometer's upper atmospheric density profiles from aerobraking, together the assumption of
hydrostatic equilibrium, to derive atmospheric pressure profiles along the spacecraft trajectory around periapsis. Two
more-or-less independent estimates of atmospheric pressure at periapsis are derived, one from the inbound leg of the
atmospheric pass, the other from the outbound leg. Differences between the two estimates imply an error in the assumption of
hydrostatic equilibrium. The primary cause of deviations from hydrostatic equilibrium is atmospheric winds and we use the
deviations to obtain an order-of-magnitude estimate of variations in wind speeds in the martian upper atmosphere.
The pressure and density profiles, together with an equation of state, give temperature profiles along the spacecraft
trajectory around periapsis. These reveal the latitudinal and diurnal behaviours of upper atmospheric temperatures.
When the spacecraft orbit was such that the same portion of the atmosphere was sampled at intervals of one martian day for a
period of several days, all three types of profiles display variability due solely to the one day interval between
measurements. We characterize latitudinal and diurnal effects on this variability.
Individual density profiles show deviations from an ideal exponential atmosphere, primarily in the form of wavelike
oscillations about the ideal case. We characterize the wavelengths and amplitudes of these oscillations and their dependences
on altitude, latitude, and time of day.
UR: http://www.lpl.arizona.edu/(tilde)withers/
DE: 5409 Atmospheres--structure and dynamics
DE: 6225 Mars
DE: 0343 Planetary atmospheres (5405, 5407, 5409, 5704, 5705, 5707)
SC: P
MN: 2002 Spring Meeting