Thursday, December 25, 2014

3D Atmospheric Simulation of Warm and Hot Jupiters

Three-dimensional Atmospheric Circulation of Warm and Hot Jupiters: Effects of Orbital Distance, Rotation Period, and Non-Synchronous Rotation


Showman et al


Efforts to characterize extrasolar giant planet (EGP) atmospheres have so far emphasized planets within 0.05 AU of their stars. Despite this focus, known EGPs populate a continuum of orbital separations from canonical hot Jupiter values (0.03-0.05 AU) out to 1 AU and beyond. Unlike typical hot Jupiters, these more distant EGPs will not in general be synchronously rotating. In anticipation of observations of this population, we here present three-dimensional atmospheric circulation models exploring the dynamics that emerge over a broad range of rotation rates and incident stellar fluxes appropriate for warm and hot Jupiters. We find that the circulation resides in one of two basic regimes. On typical hot Jupiters, the strong day-night heating contrast leads to a broad, fast superrotating (eastward) equatorial jet and large day-night temperature differences. At faster rotation rates and lower incident fluxes, however, the day-night heating gradient becomes less important, and baroclinic instabilities emerge as a dominant player, leading to eastward jets in the midlatitudes, minimal temperature variations in longitude, and, in many cases, weak winds at the equator. Our most rapidly rotating and least irradiated models exhibit multiple eastward jets in each hemisphere--similar to the jets on Jupiter and Saturn--and illuminate the dynamical continuum between highly irradiated EGPs and the weakly irradiated giant planets of our own Solar System. We present infrared (IR) light curves and spectra of these models, which show that the amplitude and offset of the IR phase variation, as well as the shape of the spectra, depend significantly on incident flux and rotation rate. This provides a way to identify the regime transition in future observations and suggests that, in some cases, IR light curves can provide constraints on the rotation rate of non-synchronously rotating planets.

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