Gravity Waves on Hot Extrasolar Planets. I. Propagation and Interaction With the Background

Watkins, C.; Cho, J. Y-K.

doi:10.1088/0004-637x/714/1/904

Cited by 38 publications

(35 citation statements)

References 34 publications

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“…Similarly, heating and fluctuations induced by gravity waves (including tides), which are also not included, may appreciably affect some of the estimates reported here (Watkins & Cho 2010).…”

Section: Resultsmentioning

confidence: 87%

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Ionization of Extrasolar Giant Planet Atmospheres

Koskinen

Cho

Achilleos

et al. 2010

ApJ

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Many extrasolar planets orbit close in and are subject to intense ionizing radiation from their host stars. Therefore, we expect them to have strong, and extended, ionospheres. Ionospheres are important because they modulate escape in the upper atmosphere and can modify circulation, as well as leave their signatures, in the lower atmosphere. In this paper, we evaluate the vertical location Z I and extent D I of the EUV ionization peak layer. We find that Z I ≈ 1-10 nbar-for a wide range of orbital distances (a = 0.047-1 AU) from the host star-and D I /H p 15, where H p is the pressure scale height. At Z I , the plasma frequency is ∼80-450 MHz, depending on a. We also study global ion transport, and its dependence on a, using a three-dimensional thermosphere-ionosphere model. On tidally synchronized planets with weak intrinsic magnetic fields, our model shows only a small, but discernible, difference in electron density from the dayside to the nightside (∼9 × 10 13 m −3 to ∼2 × 10 12 m −3 , respectively) at Z I . On asynchronous planets, the distribution is essentially uniform. These results have consequences for hydrodynamic modeling of the atmospheres of close-in extrasolar giant planets.

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Section: Resultsmentioning

confidence: 87%

“…If similar values prevail on an EGP, its homopause would be located between 1 and 10 μbar. However, K τ can be higher than the Jovian value for extrasolar planets-especially for close-in EGPs, due to the larger H p and possible stronger turbulent velocity (Watkins & Cho 2010).…”

Section: The Upper and Lower Boundariesmentioning

confidence: 90%

Ionization of Extrasolar Giant Planet Atmospheres

Koskinen

Cho

Achilleos

et al. 2010

ApJ

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“…We have checked that the spatial distribution of the temperature above 1 bar is almost identical during the two phases (not shown) and cannot be responsible for the jet velocity decrease. It is instead likely that the small-scale velocity fluctuations associated with the vertical shear instability act as a form of drag that slows down the jet, possibly mediated by gravity waves (see Watkins & Cho 2010) and, as shown above, by shocks, both excited by the vertical shear instability. Given the limitations of the numerical setup used here, a detailed and quantitative investigation of this possibility is beyond the scope of this paper, but opens up the possibility of developing a physically motivated subgrid scale model for the dissipation in the atmosphere of hot Jupiters that could be incorporated into traditional GCMs.…”

Section: Dissipation In the Deep Atmosphere And Implications For The mentioning

confidence: 94%

Shear-driven instabilities and shocks in the atmospheres of hot Jupiters

Fromang

Leconte

Heng

2016

A&A

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Context. General circulation models of the atmosphere of hot Jupiters have shown the existence of a supersonic eastward equatorial jet. These results have been obtained using numerical schemes that filter out vertically propagating sound waves and assume vertical hydrostatic equilibrium, or were acquired with fully compressive codes that use large dissipative coefficients. Aims. We remove these two limitations and investigate the effects of compressibility on the atmospheric dynamics by solving the standard Euler equations. Methods. This was done by means of a series of simulations performed in the framework of the equatorial β-plane approximation using the finite-volume shock-capturing code RAMSES. Results. At low resolution, we recover the classical results described in the literature: we find a strong and steady supersonic equatorial jet of a few km s −1 that displays no signature of shocks. We next show that the jet zonal velocity depends significantly on the grid meridional resolution. When this resolution is fine enough to properly resolve the jet, the latter is subject to a Kelvin-Helmholtz instability. The jet zonal mean velocity displays regular oscillations with a typical timescale of a few days and a significant amplitude of about 15% of the jet velocity. We also find compelling evidence for the development of a vertical shear instability at pressure levels of a few bars. It seems to be responsible for an increased downward kinetic energy flux that significantly affects the temperature of the deep atmosphere and appears to act as a form of drag on the equatorial jet. This instability also creates velocity fluctuations that propagate upward and steepen into weak shocks at pressure levels of a few mbars. Conclusions. We conclude that hot-Jupiter equatorial jets are potentially unstable to both a barotropic Kelvin-Helmholtz instability and a vertical shear instability. Upon confirmation using more realistic models, these two instabilities could result in significant time variability of the atmospheric winds, may provide a small-scale dissipation mechanism in the flow, and might have consequences for the internal evolution of hot Jupiters.

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“…Brightness maps Majeau et al 2012) and wind velocities (Snellen et al 2010) are now accessible, and constraints on the composition are becoming available, but large uncertainties remain. Observations indicate a hotspot shifted eastward of the substellar point Majeau et al 2012) and temperature contrasts smaller than what is expected for these planets without winds (Knutson et al , 2009, indicating transport of heat from the day-side to the night-side (Watkins & Cho 2010;Perez-Becker & Showman 2013). HD 209458b appears to have a temperature inversion in its upper atmosphere Burrows et al 2007) while HD 189733b does not Barman 2008;Knutson et al 2009), indicating that, despite similar orbital properties, hot Jupiters may have very different circulation patterns that still need to be understood.…”

Section: Introductionmentioning

confidence: 93%

Accuracy tests of radiation schemes used in hot Jupiter global circulation models

Amundsen

Baraffe

Tremblin

et al. 2014

A&A

167

229

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The treatment of radiation transport in global circulation models (GCMs) is crucial for correctly describing Earth and exoplanet atmospheric dynamics processes. The two-stream approximation and correlated-k method are currently state-of-the-art approximations applied in both Earth and hot Jupiter GCM radiation schemes to facilitate the rapid calculation of fluxes and heating rates. Their accuracy have been tested extensively for Earth-like conditions, but verification of the methods' applicability to hot Jupiter-like conditions is lacking in the literature. We are adapting the UK Met Office GCM, the Unified Model (UM), for the study of hot Jupiters, and present in this work the adaptation of the Edwards-Slingo radiation scheme based on the two-stream approximation and the correlated-k method. We discuss the calculation of absorption coefficients from high-temperature line lists and highlight the large uncertainty in the pressure-broadened line widths. We compare fluxes and heating rates obtained with our adapted scheme to more accurate discrete ordinate (DO) line-by-line (LbL) calculations ignoring scattering effects. We find that, in most cases, errors stay below 10% for both heating rates and fluxes using ∼10 k-coefficients in each band and a diffusivity factor D = 1.66. The two-stream approximation and the correlated-k method both contribute non-negligibly to the total error. We also find that using band-averaged absorption coefficients, which have previously been used in radiative-hydrodynamical simulations of a hot Jupiter, may yield errors of ∼100%, and should thus be used with caution.

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Gravity Waves on Hot Extrasolar Planets. I. Propagation and Interaction With the Background

Cited by 38 publications

References 34 publications

Ionization of Extrasolar Giant Planet Atmospheres

Ionization of Extrasolar Giant Planet Atmospheres

Shear-driven instabilities and shocks in the atmospheres of hot Jupiters

Accuracy tests of radiation schemes used in hot Jupiter global circulation models

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