Analytical Models of Exoplanetary Atmospheres. I. Atmospheric Dynamics via the Shallow Water System

Heng, Kevin; Workman, Jared C.

doi:10.1088/0067-0049/213/2/27

Cited by 66 publications

(48 citation statements)

References 39 publications

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“…This makes them inaccurate at high latitudes, and difficult to compare directly to real planets. Solutions on the beta-plane in other studies are similar to solutions in spherical coordinates (Showman & Polvani 2011) (Heng & Workman 2014), which suggests that its limitations are not too problematic.…”

Section: Forced Solutions In Shear Flowmentioning

confidence: 62%

“…The beta-plane system approximates the Coriolis parameter as linear, which is only accurate at low latitudes but leads to more intuitive and useful solutions than the full spherical geometry. We solve the equations in a spherical geometry in Section 5, and show that the betaplane approximation leads to very similar solutions, as in other studies of the atmospheres of tidally locked planets (Showman & Polvani 2011) (Heng & Workman 2014).…”

Section: Linearized Shallow-water Equations In Zero Flow On the Beta-mentioning

confidence: 62%

“…This allows an analytic solution but is not physically justified. Radiative damping in the shallow-water equations has a clear physical basis, but linear dynamical damping does not, apart from effects like eddy viscosity, MHD damping, or extra nonlinear terms (Heng & Workman 2014). In this section, we suggest that al-though the damping rates could be very different in reality, this does not alter the overall form of the solution.…”

Section: Effect Of Dampingmentioning

confidence: 90%

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Wave-mean Flow Interactions in the Atmospheric Circulation of Tidally Locked Planets

Hammond

Pierrehumbert

2018

ApJ

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We use a linear shallow-water model to investigate the global circulation of the atmospheres of tidally locked planets. Simulations, observations, and simple models show that if these planets are sufficiently rapidly rotating, their atmospheres have an eastward equatorial jet and a hot-spot east of the substellar point. We linearize the shallow-water model about this eastward flow and its associated height perturbation. The forced solutions of this system show that the shear flow explains the form of the global circulation, particularly the hot-spot shift and the positions of the cold standing waves on the night-side.We suggest that the eastward hot-spot shift seen in observations and 3D simulations of these atmospheres is caused by the zonal flow Doppler-shifting the stationary wave response eastwards, summed with the height perturbation from the flow itself. This differs from other studies which explained the hot-spot shift as pure advection of heat from air flowing eastward from the substellar point, or as equatorial waves travelling eastwards. We compare our solutions to simulations in our climate model Exo-FMS, and show that the height fields and wind patterns match.We discuss how planetary properties affect the global circulation, and how they change observables such as the hot-spot shift or day-night contrast. We conclude that the wave-mean flow interaction between the stationary planetary waves and the equatorial jet is a vital part of the equilibrium circulation on tidally locked planets.

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Section: Forced Solutions In Shear Flowmentioning

confidence: 62%

Section: Linearized Shallow-water Equations In Zero Flow On the Beta-mentioning

confidence: 62%

Section: Effect Of Dampingmentioning

confidence: 90%

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Wave-mean Flow Interactions in the Atmospheric Circulation of Tidally Locked Planets

Hammond

Pierrehumbert

2018

ApJ

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“…In our simple theory we utilized a linear (Rayleigh) drag, on both the zonal and meridional components of the wind. Note that small-scale turbulence (Li & Goodman 2010), shocks (Heng 2012), and Lorentz forces (Batygin et al 2013;Rauscher & Menou 2013;Heng & Workman 2014;Rogers & Komacek 2014;Rogers & Showman 2014) would, in reality, produce anisotropic drag. The strength and direction of this drag might themselves depend on parameters such as incident stellar flux, rotation rate, and atmospheric composition.…”

Section: Discussion and Directions For Future Workmentioning

confidence: 99%

“…The latter possibility may have an effect, but note that sodium (the element with the lowest ionization potential) is found in a variety of hot Jupiters regardless of equilibrium temperature . Additionally, note that the Rayleigh drag formulation that we use is at best a very rough approximation to the true effects of Lorentz forces (Perna et al 2010;Rauscher & Menou 2013;Heng & Workman 2014;Rogers & Komacek 2014). We will discuss this further in Section 4.…”

Section: Numerical Simulations With Consistent Rotation Rate and Stelmentioning

confidence: 99%

Atmospheric Circulation of Hot Jupiters: Dayside–Nightside Temperature Differences. II. Comparison with Observations

Komacek

Showman

Tan

2017

ApJ

145

183

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The full-phase infrared light curves of low-eccentricity hot Jupiters show a trend of increasing fractional daysidenightside brightness temperature difference with increasing incident stellar flux, both averaged across the infrared and in each individual wavelength band. The analytic theory of Komacek & Showman shows that this trend is due to the decreasing ability with increasing incident stellar flux of waves to propagate from day to night and erase temperature differences. Here, we compare the predictions of this theory with observations, showing that it explains well the shape of the trend of increasing dayside-nightside temperature difference with increasing equilibrium temperature. Applied to individual planets, the theory matches well with observations at high equilibrium temperatures but, for a fixed photosphere pressure of 100 mbar, systematically underpredicts the dayside-nightside brightness temperature differences at equilibrium temperatures less than 2000 K. We interpret this as being due to the effects of a process that moves the infrared photospheres of these cooler hot Jupiters to lower pressures. We also utilize general circulation modeling with double-gray radiative transfer to explore how the circulation changes with equilibrium temperature and drag strengths. As expected from our theory, the dayside-nightside temperature differences from our numerical simulations increase with increasing incident stellar flux and drag strengths. We calculate model phase curves using our general circulation models, from which we compare the broadband infrared offset from the substellar point and dayside-nightside brightness temperature differences against observations, finding that strong drag or additional effects (e.g., clouds and/or supersolar metallicities) are necessary to explain many observed phase curves.

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Atmospheric Dynamics of Hot Giant Planets and Brown Dwarfs

2020

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Groundbased and spacecraft telescopic observations, combined with an intensive modeling effort, have greatly enhanced our understanding of hot giant planets and brown dwarfs over the past ten years. Although these objects are all fluid, hydrogen worlds with stratified atmospheres overlying convective interiors, they exhibit an impressive diversity of atmospheric behavior. Hot Jupiters are strongly irradiated, and a wealth of observations constrain the day-night temperature differences, circulation, and cloudiness. The intense stellar irradiation, presumed tidal locking and modest rotation leads to a novel regime of strong day-night radiative forcing. Circulation models predict large day-night temperature differences, global-scale eddies, patchy clouds, and, in most cases, a fast eastward jet at the equator—equatorial superrotation. The warm Jupiters lie farther from their stars and are not generally tidally locked, so they may exhibit a wide range of rotation rates, obliquities, and orbital eccentricities, which, along with the weaker irradiation, leads to circulation patterns and observable signatures predicted to differ substantially from hot Jupiters. Brown dwarfs are typically isolated, rapidly rotating worlds; they radiate enormous energy fluxes into space and convect vigorously in their interiors. Their atmospheres exhibit patchiness in clouds and temperature on regional to global scales—the result of modulation by large-scale atmospheric circulation. Despite the lack of irradiation, such circulations can be driven by interaction of the interior convection with the overlying atmosphere, as well as self-organization of patchiness due to cloud-dynamical-radiative feedbacks. Finally, irradiated brown dwarfs help to bridge the gap between these classes of objects, experiencing intense external irradiation as well as vigorous interior convection. Collectively, these diverse objects span over six orders of magnitude in intrinsic heat flux and incident stellar flux, and two orders of magnitude in rotation rate—thereby placing strong constraints on how the circulation of giant planets (broadly defined) depend on these parameters. A hierarchy of modeling approaches have yielded major new insights into the dynamics governing these phenomena.

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Analytical Models of Exoplanetary Atmospheres. I. Atmospheric Dynamics via the Shallow Water System

Cited by 66 publications

References 39 publications

Wave-mean Flow Interactions in the Atmospheric Circulation of Tidally Locked Planets

Wave-mean Flow Interactions in the Atmospheric Circulation of Tidally Locked Planets

Atmospheric Circulation of Hot Jupiters: Dayside–Nightside Temperature Differences. II. Comparison with Observations

Atmospheric Dynamics of Hot Giant Planets and Brown Dwarfs

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