Irradiated Atmospheres I: Heating by Vertical-Mixing Induced Energy Transport

TL;DR

This paper proposes that vertical mixing in hot Jupiter atmospheres can explain observed temperature profiles and inversions without needing strong absorbers like TiO and VO, by introducing the concept of radiative-mixing equilibrium.

Contribution

It introduces a new model incorporating vertical mixing-driven energy transport (radiative-mixing equilibrium) to explain atmospheric thermal features in hot Jupiters, challenging previous assumptions.

Findings

Vertical mixing can induce temperature inversions in hot Jupiter atmospheres.

The atmospheric temperature-pressure profile of HD 209458b fits well with a specific $K_{zz}$ profile.

Vertical mixing affects thermal profiles and reduces estimated mixing coefficients compared to prior models.

Abstract

Observations have revealed unique temperature profiles in hot Jupiter atmospheres. We propose that the energy transport by vertical mixing could lead to such thermal features. In our new scenario, strong absorbers, TiO and VO are not necessary. Vertical mixing could be naturally excited by atmospheric circulation or internal gravity wave breaking. We perform radiative transfer calculations by taking into account the vertical mixing driven energy transport. The radiative equilibrium (RE) is replaced by radiative-mixing equilibrium (RME). We investigate how the mixing strength, $K_{\rm zz}$, affects the atmospheric temperature-pressure profile. Strong mixing can heat the lower atmosphere and cool the upper atmosphere. This effect has important effects on the atmosphere thermal features that would form without mixing. In certain circumstances, it can induce temperature inversions in scenarios where the temperature monotonically increases with increasing pressure under conditions of lower thermal band opacity. Temperature inversions show up as $K_{\rm zz}$ increases with altitude due to shear interaction with the convection layer. The atmospheric thermal structure of HD~209458b can be well fitted with $K_{\rm zz} \propto (P/1\ {\rm bar})^{-1/2}\ {\rm cm}^{2} \ {\rm s}^{-1}$. Our findings suggest vertical mixing promotes temperature inversions and lowers $K_{\rm zz}$ estimates compared to prior studies. Incorporating chemical species into vertical mixing will significantly affect the thermal profile due to their temperature sensitivity.