Semi-Transparent Shear Turbulence in Hot Jupiter Atmospheres

Abstract

Turbulent transport driven by secular shear instabilities can lead to enhanced vertical mixing in hot Jupiter atmospheres, impacting their cloudiness, chemistry and overall vertical structure. We discuss the turbulent regime expected and evaluate theoretical uncertainties on the strength of the vertical mixing (i.e, $K_{\mathrm{zz}}$ values). We focus our work on three well-studied hot Jupiters with a hierarchy of atmospheric temperatures: HD189733b ($T_{\mathrm{eq}}\simeq 1200$K), HD209458b ($T_{\mathrm{eq}}\simeq 1450$K) and Kepler7b ($T_{\mathrm{eq}}\simeq 1630$K). $K_{\mathrm{zz}}$ uncertainties are large. They are dominated by i) the poorly understood magnitude of turbulent transport and ii) the semi-transparent nature of shear turbulence near the planetary photosphere. Using a specific Moore-Spiegel instability threshold, we infer that the cooler HD189733b is not subject to enhanced mixing from semi-transparent shear turbulence while the daysides of the hotter Kepler7b and (marginally so) HD209458b are. Enhanced vertical mixing is generally expected to manifest on hot enough exoplanets, with $T_{\mathrm{eq}}>1500-1600$K. On a given planet, day and night $K_{\mathrm{zz}}$ profiles can differ by an order of magnitude or more. Vertical mixing is slightly favoured in equatorial regions, where the atmospheric zonal shear is strongest. In all three planetary cases studied, momentum feedback on the atmospheric mean flow is minor to negligible.

MNRAS accepted

References in corpus (12)

• On the radiative equilibrium of irradiated planetary atmospheres
• Observing transiting planets with JWST -- Prime targets and their synthetic spectral observations
• Atmospheric Dynamics of Hot Exoplanets
• Effects of a fully 3D atmospheric structure on exoplanet transmission spectra: retrieval biases due to day-night temperature gradients
• Chemical Transport and Spontaneous Layer Formation in Fingering Convection in Astrophysics
• Exploring Biases of Atmospheric Retrievals in Simulated JWST Transmission Spectra of Hot Jupiters
• Modeling the effects of inhomogeneous aerosols on the hot Jupiter Kepler-7b's atmospheric circulation
• Turbulent transport in radiative zones of stars
• Overcast on Osiris: 3D radiative-hydrodynamical simulations of a cloudy hot Jupiter using the parameterised, phase-equilibrium cloud formation code EddySed
• Turbulent transport by diffusive stratified shear flows: from local to global models. Part I: Numerical simulations of a stratified plane Couette flow
• Horizontal shear instabilities at low Prandtl number
• Hot Jupiter Atmospheric Flows at High Resolution

Cited by in corpus (4)

• A Direct Comparison between the use of Double Gray and Multiwavelength Radiative Transfer in a General Circulation Model with and without Radiatively Active Clouds
• An extensively validated C/H/O/N chemical network for hot exoplanet disequilibrium chemistry
• Magnetic winding and turbulence in ultra-hot Jupiters
• Compositional Turbulence and Layering in the Gaseous Envelopes of Forming Planets