ATMOSPHERIC CIRCULATION OF HOT JUPITERS: COUPLED RADIATIVE-DYNAMICAL GENERAL CIRCULATION MODEL SIMULATIONS OF HD 189733b and HD 209458b

Abstract

We present global, three-dimensional numerical simulations of HD 189733b and HD 209458b that couple the atmospheric dynamics to a realistic representation of non-gray cloud-free radiative transfer. The model, which we call the Substellar and Planetary Atmospheric Radiation and Circulation (SPARC) model, adopts the MITgcm for the dynamics and uses the radiative model of McKay, Marley, Fortney, and collaborators for the radiation. Like earlier work with simplified forcing, our simulations develop a broad eastward equatorial jet, mean westward flow at higher latitudes, and substantial flow over the poles at low pressure. For HD 189733b, our simulations without TiO and VO opacity can explain the broad features of the observed 8 and 24-µm light curves, including the modest day-night flux variation and the fact that the planet/star flux ratio peaks before the secondary eclipse. Our simulations also provide reasonable matches to the Spitzer secondary-eclipse depths at 4.5, 5.8, 8, 16, and 24 µm and the groundbased upper limit at 2.2 µm. However, we substantially underpredict the 3.6 µm secondary-eclipse depth, suggesting that our simulations are too cold in the 0.1-1 bar region. Predicted temporal variability in secondary-eclipse depths is ∼ 1% at Spitzer bandpasses, consistent with recent observational upper limits at 8 µm. We also show that nonsynchronous rotation can significantly alter the jet structure. For HD 209458b, we include TiO and VO opacity; these simulations develop a hot (> 2000 K) dayside stratosphere whose horizontal dimensions are small at depth but widen with altitude. Despite this stratosphere, we do not reproduce current Spitzer photometry of this planet. Light curves in Spitzer bandpasses show modest phase variation and satisfy the observational upper limit on day-night phase variation at 8 µm.

Disentangling degenerate solutions from primary transit and secondary eclipse spectroscopy of exoplanets

“…The high optical depths in the region above this level in a hot Jupiter give rise to an isothermal region where Figure 2. Temperature-pressure profiles of explanets HD 189733b and HD 209458b for the model atmospheres of Moses et al [32], based on the radiative transfer models of Fortney et al [33] and Fortney et al [34], and the GCM models of Showman et al [35]. Figure adapted from Moses et al [32].…”

“…The second term represents the occultation of the planet's atmosphere, which causes a drop of approximately 0.2% or less, depending on the atmospheric scale height. Note that equation (2.1) assumes that all the chords at an impact radius R intersect the same atmosphere, although there are likely latitudinal and longitudinal variations in composition, temperature and cloud cover [34,35,42]. The atmospheric transmission for a specified wavelength, Tr(R), of light through a chord, s, that is a distance R from the planet's centre can be expressed as…”

Spectroscopy of planetary atmospheres in our Galaxy

“…Cho et al 2003Cho et al , 2008Showman et al 2009;Showman and Polvani 2011;Rauscher et al 2008aRauscher et al , 2008bThrastarson and Cho 2010).…”

The Dawes Review 3: The Atmospheres of Extrasolar Planets and Brown Dwarfs

“…A widely used appoach in Earth atmosphere modelling is the correlated-k (or k-distribution) method (Goody et al 1989), which allows the use of larger wavelength bins while retaining accuracy. Recently correlated-k techniques have been used in exoplanet retrieval models (Lee, Fletcher, & Irwin 2012) and in hot Jupiter GCMs (Showman et al 2009). …”