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C. S. Cooper, A. P. Showman (University of Arizona / Lunar and Planetary Lab)
We investigate here the atmosphere of the transiting extrasolar giant planet HD 209458b. The heavy irradiation from the nearby star stabilizes the atmosphere, producing a deep radiative zone extending to pressures of 1800 bars at the object's estimated age of 5.1 Gyr.
In this work, we use a primitive equation model adapted from the atmospheric sciences to simulate the dynamics of the atmosphere of HD 209458b within the extended radiative zone. The simulations employ a scheme for Newtonian cooling to approximate the radiative transfer at depth. In this scheme, the temperature field is relaxed to the temperature profile in radiative equilibrium. We present simulations demonstrating the flow geometry for a range of assumptions about the radiative equilibrium temperature profile.
Our simulations show---in general agreement with the predictions of Showman & Guillot (2002)---fast equatorial jets of ~3 km/s at altitude (10-1000 mb), which approach the speed of sound in the fluid. At these low pressures, the hottest regions of the atmosphere are blown downstream from the substellar point where the planet receives the highest irradiation. Deeper down (>10 bars), wind velocities decrease and the equatorial jet gives way to a weak meridional flow and relatively uniform temperature profile. The simulations allow us to predict variations in the infrared light curve, which is in principle measurable with sufficiently sensitive instruments. We also diagnose the hypothesis that the object's evolution has been affected by the dissipation of atmospheric kinetic energy into the deep interior.
This research is supported by NSF grant AST-0206269, NASA Ames Research Center Cooperative Agreement (NCC 2-5518), and NASA GSRP NGT5-50462.
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Bulletin of the American Astronomical Society, 36 #4
© 2004. The American Astronomical Soceity.