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Tide-locked planets are planets in which tidal stresses from the host star have spun down the planet's rotation to the point where its length of sidereal day equals its length of year. In a nearly circular orbit, such planets have a permanent dayside and a permanent nightside, leading to extreme heating contrasts. In this article, the atmospheric circulations forced by this heating contrast are explored, with a focus on terrestrial planets; here, “terrestrial” refers to planets with a condensed solid or liquid surface at which most of the incident stellar radiation is absorbed and does not imply habitability in the Earthlike sense. The census of exoplanets contains many terrestrial planets that are very likely to be tide locked, including extremely hot close-orbit planets around Sunlike stars and habitable zone (and hotter) planets around lower-mass stars. The circulations are discussed in terms of fluid dynamical concepts arising from study of the Earth's tropics, supplemented by general circulation model simulations. Even in the relatively simple context of dry (noncondensing) dynamics, there are a number of important unresolved issues that require further study.
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Supplemental Video 1: An animation of the pressure field from which the snapshot in Figure 11 was taken.
Supplemental Figure 1. 500mb height field for a simulation of a tide-locked Super-Earth as described in [Pierrehumbert RT 2011], but having a 13-day orbital period. The simulation was carried out using the FOAM general circulation model used in the simulations in [Pierrehumbert RT 2011]. The atmosphere is an Earthlike N2-dominated atmosphere containing condensible water vapor and the substellar surface temperature is approximately 300K. Blue colors represent low-height cyclonic circulations, while red colors indicate high-height anticyclonic circulations. The substellar point is indicated by the small grey circle.
References
[Pierrehumbert RT 2011] A palette of climates for Gliese 581g. Ap. J. Lett., 726 doi:10.1088/2041-8205/726/1/L8.
Download Supplemental Figure 1 as a PDF.