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Jupiter's infrared image

What stir up Jupiter's unearthly jet streams and storms?

Credit: Gemini Observatory

Dr Xianyu Tan

Visitor

Research theme

  • Astronomy and astrophysics
  • Exoplanets and planetary physics

Sub department

  • Atmospheric, Oceanic and Planetary Physics

Research groups

  • Planetary Climate Dynamics
xianyu.tan@physics.ox.ac.uk
Atmospheric Physics Clarendon Laboratory, room 209 G
My Personal Website
  • About
  • Research
  • Publications

Weak Seasonality on Temperate Exoplanets Around Low-mass Stars

ArXiv 2203.1051 (2022)
Details from ArXiV

Cloud-convection feedback in brown dwarfs atmosphere

(2022)

Authors:

Maxence Lefèvre, Xianyu Tan, Elspeth KH Lee, RT Pierrehumbert
More details from the publisher
Details from ArXiV

Weak seasonality on temperate exoplanets around low-mass stars

Astrophysical Journal American Astronomical Society 926:2 (2022) 202

Abstract:

Planets with nonzero obliquity and/or orbital eccentricity experience seasonal variations of stellar irradiation at local latitudes. The extent of the atmospheric response can be crudely estimated by the ratio of the orbital timescale to the atmospheric radiative timescale. Given a set of atmospheric parameters, we show that this ratio depends mostly on the stellar properties and is independent of orbital distance and planetary equilibrium temperature. For Jupiter-like atmospheres, this ratio is ≪1 for planets around very low mass M dwarfs and ≳1 when the stellar mass is greater than about 0.6 solar mass. Complications can arise from various factors, including varying atmospheric metallicity, clouds, and atmospheric dynamics. Given the eccentricity and obliquity, the seasonal response is expected to be systematically weaker for gaseous exoplanets around low-mass stars and stronger for those around more massive stars. The amplitude and phase lag of atmospheric seasonal variations as a function of host stellar mass are quantified by idealized analytic models. At the infrared emission level in the photosphere, the relative amplitudes of thermal flux and temperature perturbations are negligible, and their phase lags are closed to −90° for Jupiter-like planets around very low mass stars. The relative amplitudes and phase lags increase gradually with increasing stellar mass. With a particular stellar mass, the relative amplitude and phase lag decrease from low- to high-infrared optical depth. We also present numerical calculations for a better illustration of the seasonal behaviors. Last, we discuss implications for the atmospheric circulation and future atmospheric characterization of exoplanets in systems with different stellar masses.
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Details from ORA
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Jet streams and tracer mixing in the atmospheres of brown dwarfs and isolated young giant planets

Monthly Notices of the Royal Astronomical Society Oxford University Press 511:4 (2022) 4861-4881

Abstract:

Observations of brown dwarfs and relatively isolated young extrasolar giant planets have provided unprecedented details to probe atmospheric dynamics in a new regime. Questions about mechanisms governing the global circulation and its fundamental nature remain to be completely addressed. Previous studies have shown that small-scale randomly varying thermal perturbations resulting from interactions between convection and the overlying stratified layers can drive zonal jet streams, waves, and turbulence. In this work, we improve upon our previous work by using a general circulation model coupled with a two-stream grey radiative transfer scheme to represent more realistic heating and cooling rates. We examine the formation of zonal jets and their time evolution, and vertical mixing of passive tracers including clouds and chemical species. Under relatively weak radiative and frictional dissipation, robust zonal jets with speeds up to a few hundred m s−1 are typical outcomes. The off-equatorial jets tend to be pressure independent, while the equatorial jets exhibit significant vertical wind shear. On the other hand, models with strong dissipation inhibit the jet formation and leave isotropic turbulence in off-equatorial regions. Quasi-periodic oscillations of the equatorial flow with periods ranging from tens of days to months are prevalent at relatively low atmospheric temperatures. Submicron cloud particles can be easily transported to several scale heights above the condensation level, while larger particles form thinner layers. Cloud decks are significantly inhomogeneous near their cloud tops. Chemical tracers with chemical time-scales >105 s can be driven out of equilibrium. The equivalent vertical diffusion coefficients, Kzz, for the global-mean tracer transport are diagnosed from our models and are typically on the order of 1–102 m2 s−1. Finally, we derive an analytic estimation of Kzz for different types of tracers under relevant conditions.
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HST/WFC3 Complete Phase-resolved Spectroscopy of White-dwarf-brown-dwarf Binaries WD 0137 and EPIC 2122

The Astronomical Journal American Astronomical Society 163:1 (2022) 17

Authors:

Yifan Zhou, Dániel Apai, Xianyu Tan, Joshua D Lothringer, Ben WP Lew, Sarah L Casewell, Vivien Parmentier, Mark S Marley, Siyi Xu, LC Mayorga
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