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.

arXiv commentMNRAS accepted

References in corpus (37)

• Modules for Experiments in Stellar Astrophysics (MESA): Giant Planets, Oscillations, Rotation, and Massive Stars
• Presupernova Evolution of Rotating Massive Stars I: Numerical Method and Evolution of the Internal Stellar Structure
• A continuum from clear to cloudy hot-Jupiter exoplanets without primordial water depletion
• Atmospheric circulation of hot Jupiters: Coupled radiative-dynamical general circulation model simulations of HD 189733b and HD 209458b
• On the radiative equilibrium of irradiated planetary atmospheres
• Characterizing transiting exoplanet atmospheres with JWST
• 3D mixing in hot Jupiter atmospheres. I. application to the day/night cold trap in HD 209458b
• Gaseous Mean Opacities for Giant Planet and Ultracool Dwarf Atmospheres over a Range of Metallicities and Temperatures
• Exoplanetary Atmospheres: Key Insights, Challenges and Prospects
• Transitions in the cloud composition of hot Jupiters
• Atmospheric circulation of tidally locked exoplanets: a suite of benchmark tests for dynamical solvers
• Observing transiting planets with JWST -- Prime targets and their synthetic spectral observations
• Magnetic Drag on Hot Jupiter Atmospheric Winds
• Atmospheric Dynamics of Hot Exoplanets
• Three-Dimensional Atmospheric Circulation Models of HD 189733b and HD 209458b with Consistent Magnetic Drag and Ohmic Dissipation
• A General Circulation Model for Gaseous Exoplanets with Double-Gray Radiative Transfer
• Magnetic Scaling Laws for the Atmospheres of Hot Giant 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
• Formation of Silicate and Titanium Clouds on Hot Jupiters
• Why is it so Cold in Here?: Explaining the Cold Temperatures Retrieved from Transmission Spectra of Exoplanet Atmospheres
• Exploring Biases of Atmospheric Retrievals in Simulated JWST Transmission Spectra of Hot Jupiters
• Exoplanet Clouds
• Global-mean Vertical Tracer Mixing in Planetary Atmospheres I: Theory and Fast-rotating Planets
• Vertical Tracer Mixing in Hot Jupiter Atmospheres
• Clouds in Three-Dimensional Models of Hot Jupiters Over a Wide Range of Temperatures I: Thermal Structures and Broadband Phase Curve Predictions
• Strong biases in retrieved atmospheric composition caused by strong day-night chemical heterogeneities
• Modeled Temperature-Dependent Clouds with Radiative Feedback in Hot Jupiter Atmospheres
• Global-mean Vertical Tracer Mixing in Planetary Atmospheres II: Tidally Locked Planets
• Circulation and Dissipation on 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
• Turbulent Vertical Mixing in Hot Exoplanet Atmospheres
• Hot Jupiter Atmospheric Flows at High Resolution

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