Atmospheric Dynamics Modeling of Venus with Realistic Topography and Structure and Comparative Modeling of Titan

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AST 0407186DowlingThe proximity of Venus to Earth makes it a major target for planetary exploration, both because it is easy to reach and because of the need to understand why Earth and its closest neighbor are so different. Several missions to Venus have returned remote sensing and in situ observations, and the vista from Earth of both Venus and Titan has dramatically improved with precise near-infrared filters and adaptive optics. History has ordered itself such that most of the modern toolsused to simulate atmospheric dynamics have been developed after the bulk of Venus spacecraft missions have been completed. The result is that all the data are fresh and the planet is an open book. Titan, about to become an open book itself, is dynamically closest to Venus because it is also a slow rotator, hence, it is traditional to pair the two for comparative studies. Furthermore, indications are that Titan's atmosphere exhibits a superrotation that is similar to that of Venus. There is heightened interest in Venus and Titan for several reasons, two being a recent credible claim for simulating the full Venus superrotation starting at rest in a low-resolution atmospheric model, and the advent of the Cassini Orbiter/ Huygens-Probe mission to Titan. Attempts to model equatorial superrotation have focused on simplified models that logically reduce andisolate the number of candidate physical processes being tested. Some numerical simulations lend support to the Gierasch mechanism wherein momentum is transported vertically as part of the Hadley-cell circulation, and to the equator by waves from instability, but there is also support for other eddy sources such as thermal tides and topographically excited gravity waves. Part of the problem is to distinguish which effects contribute most to a given altitude region. A leading detail missing from many Venus spinup models to date is topography. Venus has tall mountains, and these should generate internal-wave phenomena and modify the planetary boundary layer and the influence of the surface on the atmosphere. In this project, Dr. Timothy Dowling brings to Venus/Titan research a new tool, a high-resolution general circulation model, EPIC, which uses a hybrid isentropic/terrain-following vertical coordinate. In the first year, Dr. Dowling will begin by reproducing the superrotation results of Yamamoto and Takahashi for Venus, with additional sensitivity tests regarding the Newtonian cooling profile and the horizontal resolution, which will yield a valuable confirmation of the results. Also in Year 1, the researchers will systematically test the effects of topography on the general circulation. This work will continue into the second year. In Year 2, they will add sulfuric-acid clouds to the Venus model, taking advantage of the EPIC model's existing cloud-microphysics capabilities, and compare the model's cloud patterns with ultraviolet (UV) observations of Venus. It is anticipated that Titan will be the primary focus in the third year, as new data from the Huygens Probe and Cassini Orbiter become available. Because Venus and Titan have small Coriolis accelerations progress in understanding their atmospheric dynamics translates into advances in understanding equatorial or tropical meteorology on any planet. As in the past, the EPIC model will be made freely available as open source code, providing a new tool for Venus/Titan studies to the planetary astronomy community. On the demographic front, this project promotes an effort to expand atmospheric dynamics research in Kentucky. ***