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S. W. Bougher, J. M. Bell (U. of Michigan), D. T. Baird (UCLA and JPL), J. R. Murphy (NMSU)
New Mars spacecraft datasets and 3-D modeling capabilities are emerging to characterize the Mars thermospheric circulation patterns for the first time. Upper atmosphere wind constraints are available from recent aerobraking and Mars Express measurements. Mars Global Surveyor (1997-1999) and Mars Odyssey (2001-2002) Accelerometer datasets obtained during aerobraking operations provide density and temperature distributions over limited local time and latitude regions at lower thermospheric altitudes (~100-160 km) [e.g. Keating et al., 1998; 2002; 2003; Withers et al., 2003]. Latitudinal gradients of these fields (i.e. into the winter polar night) vary greatly with the changing Martian seasons. The winter polar warming features observed serve as a tracer of the strength and variability of the Martian thermospheric wind patterns during solstice conditions [Keating et al., 2003; Bougher et al., 2005].Accelerometer data is also being used to estimate cross-track (zonal) wind speeds in the Mars lower thermosphere (~100-130 km) [Baird et al., 2005], yielding values as large as 300-400 m/sec. Most recently, the Mars Express SPICAM instrument discovered nitric oxide (NO) nightglow spectral features in the \gamma and \delta-bands from limb observations (Ls = 74) [Bertaux et al., 2005]. These observed UV nightglow emissions are brightest in the winter polar night region. The solstice winds required to produce the Mars winter polar warming features are also responsible for transporting dayside produced N and O atoms to the nightside where radiative recombination and UV chemiluminescence occurs. These new dynamical constraints for the Martian upper atmosphere are now investigated using coupled MGCM (NASA Ames) and MTGCM (Michigan) simulations for aphelion (Ls = 90) and perihelion (Ls = 270) conditions appropriate to MGS and Odyssey aerobraking datasets described above. Seasonal variations in the thermospheric circulation, and the underlying mechanisms likely responsible for these variations, are investigated. Consistency with the NO nightglow morphology and intensities is also discussed.
The author(s) of this abstract have provided an email address for comments about the abstract: bougher@umich.edu
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Bulletin of the American Astronomical Society, 37 #3
© 2004. The American Astronomical Soceity.