Tracing the Dynamics in Venus' Upper Atmosphere.

Venus is a unique planet because its atmospheric dynamics are mainly driven by thermal heating and its very low rotation rate. Many details of the middle and upper atmospheric dynamics can be determined from observing nightside airglow emissions, which serve as effective tracers of Venus' middle and upper atmosphere global wind system. The purpose of this dissertation is to use the National Center for Atmospheric Research (NCAR) Venus Thermospheric General Circulation Model (VTGCM) to examine the underlying processes that control the thermospheric circulation of Venus by comparing simulations to observations. Most recently, Venus Express (VEX) has been monitoring key atmospheric features (O2 IR nightglow, NO UV nightglow, and nightside temperatures) of Venus. Statistical maps have been created utilizing these nightglow observations from VEX. Moreover, the O2 IR statistical map has been used to deduce a three-dimensional atomic oxygen density map, which is used to examine the implications of atomic oxygen density distributions below 140 km on the nightside. The VTGCM model has been reconstructed and revised in order to address these key nightglow observations and provide diagnostic interpretation. Specifically, the VTGCM simulations capture the statistically averaged mean state of these three key observations. The correlation between the simulation results and the VEX data sets implies a weak retrograde superrotating zonal flow (RSZ) from ~80 km to 110 km with the emergence of modest RSZ winds approaching 60 m s-1 above ~130 km. This RSZ flow is superimposed upon a strong subsolar-antisolar flow from day-to-night. VTGCM sensitivity tests were subsequently performed using two tunable parameters (nightside eddy diffusion and wave drag) to examine corresponding variability within the VTGCM and these nightglow distributions. The VTGCM also reproduces a nightside atomic oxygen density map and vertical profiles across the nightside. Both the simulated map and vertical profiles are in close agreement with VEX observations within a ~30 degree contour of the anti-solar point. The atomic oxygen vertical profiles are comparable to the data above 90 km, consistent with the corresponding O2 IR nightglow intensities. The research performed for this dissertation has determined the parametric sensitivity of the thermospheric flow around Venus.PhDAtmospheric and Space SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/84530/1/abrecht_1.pd