Temporal Variability in Hot Jupiter Atmospheres

TL;DR

This study uses idealized models to show that hot Jupiter atmospheres exhibit measurable time variability in temperature, wind speeds, and observable signals like eclipse depths and phase curves, influenced by stellar flux and magnetic effects.

Contribution

It demonstrates that hot Jupiter atmospheres are inherently variable and quantifies how this variability affects observable properties, incorporating effects of stellar flux and magnetic drag.

Findings

Atmospheric temperature varies by 0.1-1% globally.

Observable signals like eclipse depth vary by up to 2%.

Wind speeds can change by up to 10% and shift by several degrees.

Abstract

Hot Jupiters receive intense incident stellar light on their daysides, which drives vigorous atmospheric circulation that attempts to erase their large dayside-to-nightside flux contrasts. Propagating waves and instabilities in hot Jupiter atmospheres can cause emergent properties of the atmosphere to be time-variable. In this work, we study such weather in hot Jupiter atmospheres using idealized cloud-free general circulation models with double-grey radiative transfer. We find that hot Jupiter atmospheres can be time-variable at the $\sim 0.1-1\%$ level in globally averaged temperature and at the $\sim 1-10\%$ level in globally averaged wind speeds. As a result, we find that observable quantities are also time variable: the secondary eclipse depth can be variable at the $\lesssim 2\%$ level, the phase curve amplitude can change by $\lesssim 1\%$, the phase curve offset can shift by $\lesssim 5^{\circ}$, and terminator-averaged wind speeds can vary by $\lesssim 2~ \mathrm{km}~\mathrm{s}^{-1}$. Additionally, we calculate how the eastern and western limb-averaged wind speeds vary with incident stellar flux and the strength of an imposed drag that parameterizes Lorentz forces in partially ionized atmospheres. We find that the eastern limb is blueshifted in models over a wide range of equilibrium temperature and drag strength, while the western limb is only redshifted if equilibrium temperatures are $\lesssim1500~\mathrm{K}$ and drag is weak. Lastly, we show that temporal variability may be observationally detectable in the infrared through secondary eclipse observations with JWST, phase curve observations with future space telescopes (e.g., ARIEL), and/or Doppler wind speed measurements with high-resolution spectrographs.