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E. Colón, T. E. Dowling (CPL/U. Louisville)
We are conducting a series of three-dimensional sensitivity experiments to understand the influence of the Venusian topography on its general circulation. This is the first application of the EPIC model's hybrid \sigma-\theta vertical coordinate in which the terrain-following \sigma coordinate transitions smoothly into an isentropic coordinate aloft (potential temperature, \theta).
Forcing by convection, solar disturbances, and orographic effects have been cited to explain various wave signatures in Pioneer Venus, VEGA Balloon, and Magellan radio-occultation data. A mix of these wave sources is possible. Hinson and Jenkins (1995, Icarus, 114, 310-327) demonstrate that small-scale oscillations and scintillations in Magellan radio-occulation data taken on three successive orbits (3.3 hr intervals) are probably internal gravity waves located above the convecting middle cloud layer that are nearly stationary relative to the surface or the sun, citing an orographic source as a possible explanation. An example of a convective source for waves, in particular those seen in the stable layer sandwiched between the middle cloud and the lower atmosphere, is the work of Baker et al. (2000, J. Atmos. Sci., 57, 187--199 and 200--215).
We are seeking to isolate the contribution of orographic effects in the shaping of the zonal-wind profile with height, starting with the differences between no topography and the Magellan topograpy, and employing the Eliassen-Palm flux divergence, which quantifies the impact of wave forcing on mean zonal flows, as a diagnostic tool.
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