Exoplanet atmospheric dynamics

Exoplanet atmospheric dynamics includes day-night circulation, zonal jets, waves, vortices, storms, and heat redistribution under irradiation, rotation, drag, and magnetic effects.

Day-night heat redistribution transports absorbed stellar energy from an irradiated hemisphere to a dark hemisphere through atmospheric or oceanic motion. Its efficiency controls the thermal phase-curve amplitude and nightside temperature of a synchronously rotating planet.

This factor converts substellar incident flux into the representative flux used in an atmospheric model. Uniform global averaging gives $f_r=1/4$; dayside averaging gives $1/2$ if albedo is treated separately. The convention must be stated when defining an irradiation temperature.

If a fraction $ϵ$ of total absorbed stellar power reaches the night side, blackbody balance gives

A column near pressure $p$ contains mass per area of order $p/g$. Linearizing its blackbody cooling around temperature $T$ gives the estimatewhere $c_p$ is specific heat capacity at constant pressure. This estimate omits details of wavelength-dependent radiative transfer, but captures faster relaxation in hotter and lower-pressure atmospheric layers.

The atmospheric advection time over length $L$ at wind speed $U$ is ${\tau }_{\mathrm{adv}}\sim L/U$. Day-night heat redistribution tends to be efficient when this time and the relevant wave-adjustment time are shorter than the radiative relaxation time in a planetary atmosphere.

An exoplanet thermal phase curve measures infrared brightness throughout the orbit. Its amplitude constrains day-night heat redistribution, while its maximum's displacement from secondary eclipse constrains the offset of the hottest atmospheric region. Wavelength-dependent opacity makes different channels probe different pressures.

Atmospheric superrotation is an eastward equatorial jet whose angular momentum per unit mass exceeds that of the underlying solid body at the equator. Hot-Jupiter waves can transport angular momentum into the equatorial region and maintain such a jet.