Schedule Apr 02, 2010
Three-Dimensional Atmospheric Circulation of the Highly Eccentric Extrasolar Planet HD80606b
Nikole K. Lewis (Univ. Arizona)

Nikole K. Lewis, Adam P. Showman, Jonathan J. Fortney, Mark S. Marley, and Richard P. Freedman

HD80606b has the largest eccentricity (e=0.93366) of the known transiting extrasolar planet population. Because of this highly eccentric orbit, HD80606b is flash heated as it passes through the periapse, which leads to a significant increase in the overall temperature of the planet and thermal gradients that drive winds. We utilize a three-dimensional general circulation model that has been coupled to a state of the art radiative transfer model to explore the atmospheric dynamics of this eccentric hot Jupiter. For most of HD80606b's orbit, the planet maintains a fairly stable jet structure with a westward (subrotating) jet near the equator and eastward jets in the high-latitude regions. However, as the planet passes through periapse, the wind patterns change dramatically with latitude, longitude, and pressure. A shock-like feature develops on the nightside of the planet just after it passes through periapse in response to the flash heating event. Peak global wind speeds are reached ~9 hours after periapse passage and gradually decline for several weeks until the nominal wind patterns are restored. The peak atmospheric temperature averaged over latitude, longitude, and pressure is reached ~5 hours after periapse passage. However, the planet/star flux ratio as seen from Earth reaches a peak directly at periapse in all of the Spitzer IRAC bandpasses assuming a pseudo-synchronous rotation rate. In general, we find that for close-in extrasolar planets on eccentric orbits peak atmospheric temperatures and winds lag behind the peak in stellar incident radiation by several hours. Also assumptions about the geometry of these eccentric orbits with respect to Earth and the assumed rotation rate could affect the interpretation of observational data. Tests involving planetary rotation rates greater and less than the pseudo-synchronous rotation rate will be presented. HD80606b is one of the prime targets of the warm Spitzer mission and is likely to continue to be a target of interest for ground-based observations and the upcoming James Webb Space Telescope. The circulation models presented here provide important insights that will aid in the interpretation of these upcoming data.

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