Atmospheric Dynamics of Short‐Period Extrasolar Gas Giant Planets. I. Dependence of Nightside Temperature on Opacity

Abstract

More than two dozen short-period Jupiter-mass gas giant planets have been discovered around nearby solar-type stars in recent years, several of which undergo transits, making them ideal for the detection and characterization of their atmospheres. Here we adopt a three-dimensional radiative hydrodynamical numerical scheme to simulate atmospheric circulation on close-in gas giant planets. In contrast to the conventional GCM and shallow water algorithms, this method does not assume quasi-hydrostatic equilibrium, and it approximates radiation transfer from optically thin to thick regions with flux-limited diffusion. In the first paper of this series, we consider synchronously spinning gas giants. We show that a full three-dimensional treatment, coupled with rotationally modified flows and an accurate treatment of radiation, yields a clear temperature transition at the terminator. Based on a series of numerical simulations with varying opacities, we show that the nightside temperature is a strong indicator of the opacity of the planetary atmosphere. Planetary atmospheres that maintain large interstellar opacities will exhibit large day-night temperature differences, while planets with reduced atmospheric opacities due to extensive grain growth and sedimentation will exhibit much more uniform temperatures throughout their photospheres. In addition to numerical results, we present a four-zone analytic approximation to explain this dependence.

Pseudo 2D chemical model of hot-Jupiter atmospheres: application to HD 209458b and HD 189733b

“…This superrotating jet was first predicted by Showman & Guillot (2002), has been found to emerge from almost all GCM simulations of hot Jupiters (Cooper & Showman 2005;Showman et al 2008Showman et al , 2009Showman et al , 2013Dobbs-Dixon & Lin 2008;, 2012aPerna et al 2010Perna et al , 2012Heng et al 2011a,b;Lewis et al 2010;Kataria et al 2013;Parmentier et al 2013), and is also understood theoretically (Showman & Polvani 2011). A shift of the hottest point of the planet eastward from the substellar point has been directly observed in several exoplanets (Knutson et al 2007(Knutson et al , 2009a(Knutson et al , 2012Crossfield et al 2010) and interpreted as a direct (Parmentier et al 2013).…”

Accuracy tests of radiation schemes used in hot Jupiter global circulation models

“…In the past decade, GCMs have been used to study largescale circulation on hot Jupiters (Showman & Guillot 2002;Showman et al 2009;Rauscher & Menou 2012;Cho et al 2008;Thrastarson & Cho 2010;Dobbs-Dixon & Lin 2008), a class of extrasolar planets which are approximately the size of Jupiter but orbit less than 0.1 au from their parent star. These planets, thought to have tidally locked circular orbits due to strong tidal interactions between the planet and its parent star (Baraffe et al 2010), experience intense irradiation yielding a significant temperature contrast between the (permanent) 1 See http://earthsystemcog.org/projects/dcmip-2012/ day-side and night-side.…”

The unified model, a fully-compressible, non-hydrostatic, deep atmosphere global circulation model, applied to hot Jupiters

“…prevailing circumplanetary flows) to be comparable in size with the horizontal extent of the atmosphere. Despite the exotic nature of the flow regime, the adaptation of GCMs to hot Jupiters has met with success as, for example, several models have been able to demonstrate that offsets in the hot spot are consistent with redistribution from zonal (longitudinal direction) winds (Showman et al 2009;Dobbs-Dixon & Lin 2008;Dobbs-Dixon 2009). The progress of the modelling has been reviewed in Showman et al (2008 and a useful summary of the different approaches taken can be found in Dobbs-Dixon & Agol (2013).…”

“…However, the approximations involved in the primitive equations neglect the vertical acceleration of fluid parcels, and the effect of the vertical velocity on the horizontal momentum. More complete dynamical models, solving the full Navier-Stokes equations, have been applied to hot Jupiters by Dobbs-Dixon & Lin (2008), Dobbs-Dixon (2009), Dobbs-Dixon et al (2010), Dobbs-Dixon & Agol (2013), but these models include a radiative transfer scheme more simplified than the method of Showman et al (2009). Dobbs-Dixon et al (2010) includes frequency dependent radiative transfer via the introduction of only three opacity bins (and generally runs for short elapsed model times).…”