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withers

HR: 0830h
AN: P61C-0353
TI: Winds in the martian upper atmosphere from MGS aerobraking density profiles
AU: * Withers, P
EM: withers@lpl.arizona.edu
AF: University of Arizona, Lunar and Planetary Laboratory University of Arizona, Tucson, AZ 85716 United States
AU: Bougher, S W
EM: bougher@engin.umich.edu
AF: University of Michigan, Space Physics Research Laboratory AOSS Department 2455 Hayward Avenue University of Michigan, Ann Arbor, MI 48109-2143 United States
AU: Keating, G M
EM: g.m.keating@larc.nasa.gov
AF: George Washington University at NASA Langley, George Washington University at NASA Langley, MS 269, Hampton, VA 23681 United States
AB: We have used a novel technique to measure the zonal wind in the martian upper atmosphere using MGS Accelerometer aerobraking density profiles. Typical results for the northern hemisphere (NH) at about Ls=40, 115 km altitude and midafternoon local solar times (LSTs) show a westward speed of 50 to 100 m/s; those for the southern hemisphere (SH) at about Ls=80, 110 km altitude show an eastward speed of 0 to 50 m/s. Solar activity is moderate for both periods with an F10.7 index of about 140 units. In the NH, wind speed shows no dependence on longitude, decreases as latitude increases poleward, and increases as altitude increases. In the SH, repeated measurements of wind speed at fixed latitude, altitude, LST, and longitude during the 8:1 resonance between MGS's orbit and Mars' rotation show a significant dependence of wind speed on longitude. At 20E longitude the typical wind speed is 50 m/s westward, whereas at 335E it is 120 m/s eastward. The dependence of wind speed on latitude and altitude is difficult to examine, because periapsis altitude steadily decreased as periapsis precessed poleward. The two variables are strongly correlated. In some longitude regions, eastward wind speeds increase as periapsis moves poleward and downward, but in others the eastward wind speeds stay constant. At 60S latitude and nighttime LSTs, wind speeds differ from their daytime values. Nighttime wind speeds at a given longitude show much less variability than their daytime counterparts. These results will be compared to MTGCM simulations. Other applications of this technique will be suggested.
UR: http://www.lpl.arizona.edu/~withers
DE: 0343 Planetary atmospheres (5405, 5407, 5409, 5704, 5705, 5707)
DE: 0394 Instruments and techniques
DE: 3394 Instruments and techniques
DE: 5409 Atmospheres--structure and dynamics
DE: 6225 Mars
SC: Planetary Sciences [P]
MN: 2002 Fall Meeting