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STP12 Abstracts Berlin, 12 - 16 July 2010 SCOSTEP Symposium 2010 Compositional and Dissipative Effects on Wave Propagation in a Diffusively Separated Atmosphere Walterscheid Richard 1 , Hickey Michael 2 , Schubert Gerald 3 1 The Aerospace Corporation, 2 Embry-Riddle Aeronautical University, 3 UCLA We present results from a new model that simulates acoustic-gravity wave propagation in a binary gas mixture of atomic oxygen and molecular nitrogen. The model includes the effects of molecular viscosity and thermal conduction. Compositional effects include the collisional transfer of heat and momentum between gases and the effects that one gas has on the viscosity and thermal conduction of the other. The individual constituents have different phase and amplitude dependencies with altitude owing to the individual characteristics of the gases (scale heights and vertical wavelengths). We find that dissipation reduces the phase differences between constituents relative to those with thermal and momentum coupling acting alone [del Genio et al., 1978]. Compositional effects reduce the effective dynamic viscosity and thermal conduction for individual constituents in proportion to their mixing ratios; the less abundant the constituent the weaker the dissipation. This has a significant effect on the amplitudes of wave quantities for the individual gases relative to each other. At altitudes where thermal and momentum coupling is small the upward flux of energy and momentum is partitioned between the constituents. The total gas result gotten by summing over the individual gases differs significantly from the results of a single gas model with compositional effects included by means of height-variable time-independent mean molecular weight (the usual approach). The accuracy of single gas models can be significantly improved by allowing the mean molecular weight M to be conserved following parcel displacement, whence the perturbation value of M is nonzero. We discuss the implications of these results for gravity wave propagation in the thermosphere. Del Genio, A. D., J. M. Straus, and G. Schubert, Effects of wave-induced diffusion on thermospheric acoustic-gravity waves, Geophys. Res. Lett., 5, 265, 1978.
STP12 Abstracts Berlin, 12 - 16 July 2010 SCOSTEP Symposium 2010 High Latitude Thermal Cells Induced by Ion Drag Driven Gyres Walterscheid Richard 1 , Crowley Geoff 2 1 The Aerospace Corporation, 2 ASTRA Under typical conditions, the ions driven into motion by the high latitude electric field generates a pair of counter-rotating anticyclonic and cyclonic gyres in the neutral wind circulation. When viscous and ion-drag forces are not too strong dynamical adjustment of the atmosphere acts to bring the winds into an approximate gradient wind balance between the inertial forces (Coriolis and centrifugal) and the pressure gradient. These forces act in the same direction for cyclonic gyres and in the opposite direction for anticyclonic gyres. When the flow is not too strong or too curved the Coriolis force is dominant and dynamical adjustment gives a pair of high (warm) and low (cold) pressure cells, associated respectively with the anticyclonic and cyclonic gyres. However, when the flow is sufficiently rapid the centrifugal force dominates and both gyres give relatively cold low pressure cells. The thermal changes induced by dynamics are adiabatic and are in addition to the changes induced by the diabatic heat sources. We have examined the balance of forces with a 3-D general circulation model of the upper atmosphere (TIME-GCM). We infer the balance of forces normal to the motion (centrifugal, Coriolis and pressure gradient) forces. We have examined the balance of forces and the pressure and thermal response to these forces during quiet and active times. The quiet-time structure is radically changed when the atmosphere is spun up into rapid motion during active periods. During active periods structures form that are more complicated than the structure of the forcing itself. Centers of relative low density air are found on both the dawn and dusk sides with a trough of low density air over the pole connecting them. The intrusion of low density air over the pole splits the region of high density air that exists under quiet conditions giving two high density centers, one toward the midnight side and other toward the noon side. This gives the four cell pattern simulated by Crowley et al., 1989, 1996. We find that this structure evolves when the flow is too rapid to sustain the quiet-time warm high-pressure anticyclonic cells. Crowley, G., B. A. Emery, R. G. Roble, H. C. Carlson, and D. J. Knipp (1989), Thermospheric dynamics during September 18 – 19, 1984: 1. Model simulations, J. Geophys. Res., 94, 16,925– 16,944. Crowley, G., J. Schoendorf, R. G. Roble, and F. A. Marcos (1996), Cellular structures in the high-latitude thermosphere, J. Geophys. Res., 101, 211–223, doi:10.1029/95JA02584.
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scostep 2010 (stp12) - Leibniz-Institut für Atmosphärenphysik an der ...

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