The Atmospheric Circulation and Evolution of Close-In Extrasolar Gas Giant Planets

Abstract

The atmospheres of extrasolar gas giants that receive strong stellar irradiation, or “hot Jupiters,” are beginning to be characterized as a population. Spectro- photometric full-phase light curves of hot Jupiters allow for basic inferences of their atmospheric circulation, providing two key observables. First, they measure the amplitude of brightness variation, which has shown that the fractional brightness temperature difference between the dayside and nightside in the atmospheres of these tidally locked planets can approach unity. Additionally, each planet has a significant observed offset of the brightest point in their light curve, and offsets in the infrared ubiquitously occur before secondary eclipse. These infrared offsets are best explained by strong (~ a few km/s) eastward winds in hot Jupiter atmospheres. Motivated by these observations, I have developed a first-principles analytic theory that predicts dayside-nightside temperature differences and horizontal and vertical wind speeds as a function of incident stellar flux, rotation rate, frictional drag strength, and atmospheric pressure level. To complement and compare with this theory, I have performed a hierarchy of three-dimensional numerical simulations of the atmospheric circulation to explore changes with incident stellar flux, rotation rate, and drag strength. Both the theory and numerical simulations predict that the dayside-nightside temperature differences of hot Jupiters and their wind speeds should increase with increasing incident stellar flux and decrease with increasing drag strength. So far, this has been hinted at in the observed sample of hot Jupiter phase curves, but I predict that these broad trends will be robust with a larger observed population. I extend this theory to estimate vertical mixing rates, which is critical for understanding the impact of clouds and disequilibrium chemistry on observations of hot Jupiters. I find good agreement between numerically simulated vertical mixing rates and analytic theory, allowing one to use these theoretically predicted vertical mixing rates as input for one-dimensional models of cloud formation and disequilibrium chemistry in hot Jupiter atmospheres. I use this same suite of simulations to diagnose observable time-variability in the atmospheres of hot Jupiters, finding that purely hydrodynamic mechanisms induce significant variability in phase curve offset, amplitude, and secondary eclipse depth. Lastly, as many hot Jupiters are “inflated,” with radii larger than those in standard irradiated evolution models, I use one-dimensional planetary structure modeling to determine the effect that the atmospheric circulation has on the evolution of the planet by transporting heat toward the interior. I find that if the atmospheric circulation can deposit heat at pressures ??greater than 100 bars and if this heat is applied early (within ~ 10 Myr of formation) and persists throughout their evolution, then atmospheric circulation can explain the inflated radii of the bulk of the hot Jupiter sample.