Diurnal Thermal Tides in a Non-synchronized Hot Jupiter

TL;DR

This study analyzes how diurnal thermal tides in a non-synchronized hot Jupiter excite internal waves and influence angular momentum transfer, affecting the planet's internal dynamics and rotation.

Contribution

It provides a linear analysis of thermal tide-induced internal waves and their role in angular momentum transfer in non-synchronized hot Jupiters, considering Coriolis effects.

Findings

Diurnal thermal forcing can excite internal waves when period exceeds sound crossing time.

Coriolis effects lead to excitation of g modes and Rossby waves depending on asynchrony.

Internal waves can transfer angular momentum, creating vertical shear in the planet.

Abstract

We perform a linear analysis to investigate the dynamical response of a non-synchronized hot Jupiter to stellar irradiation. In this work, we consider the diurnal Fourier harmonic of the stellar irradiation acting at the top of a radiative layer of a hot Jupiter with no clouds and winds. In the absence of the Coriolis force, the diurnal thermal forcing can excite internal waves propagating into the planet's interior when the thermal forcing period is longer than the sound crossing time of the planet's surface. When the Coriolis effect is taken into consideration, the latitude-dependent stellar heating can excite weak internal waves (g modes) and/or strong baroclinic Rossby waves (buoyant r modes) depending on the asynchrony of the planet. When the planet spins faster than its orbital motion (i.e. retrograde thermal forcing), these waves carry negative angular momentum and are damped by radiative loss as they propagate downwards from the upper layer of the radiative zone. As a result, angular momentum is transferred from the lower layer of the radiative zone to the upper layer and generates a vertical shear. We estimate the resulting internal torques for different rotation periods based on the parameters of HD 209458b.