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Title: UTILITY OF THE WEAK TEMPERATURE GRADIENT APPROXIMATION FOR EARTH-LIKE TIDALLY LOCKED EXOPLANETS

Planets in M dwarf stars' habitable zones are likely to be tidally locked with orbital periods of the order of tens of days. This means that the effects of rotation on atmospheric dynamics will be relatively weak, which requires small horizontal temperature gradients above the boundary layer of terrestrial atmospheres. An analytically solvable and dynamically consistent model for planetary climate with only three free parameters can be constructed by making the weak temperature gradient (WTG) approximation, which assumes temperatures are horizontally uniform aloft. The extreme numerical efficiency of a WTG model compared to a three-dimensional general circulation model (GCM) makes it an optimal tool for Monte Carlo fits to observables over parameter space. Additionally, such low-order models are critical for developing physical intuition and coupling atmospheric dynamics to models of other components of planetary climate. The objective of this paper is to determine whether a WTG model provides an adequate approximation of the effect of atmospheric dynamics on quantities likely to be observed over the next decade. To do this, we first tune a WTG model to GCM output for an Earth-like tidally locked planet with a dry, 1 bar atmosphere, then generate and compare the expected phase curves ofmore » both models. We find that differences between the two models would be extremely difficult to detect from phase curves using the James Webb Space Telescope. This result demonstrates the usefulness of the WTG approximation when used in conjunction with GCMs as part of a modeling hierarchy to understand the climate of remote planets.« less
Authors:
 [1] ;  [2]
  1. Department of Astronomy and Astrophysics, University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637 (United States)
  2. Department of the Geophysical Sciences, University of Chicago, 5734 South Ellis Avenue, Chicago, IL 60637 (United States)
Publication Date:
OSTI Identifier:
22136542
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal Letters; Journal Volume: 774; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; APPROXIMATIONS; BOUNDARY LAYERS; CLIMATES; DWARF STARS; EARTH ATMOSPHERE; GENERAL CIRCULATION MODELS; MATHEMATICAL SPACE; MONTE CARLO METHOD; PLANETS; ROTATION; TELESCOPES; TEMPERATURE GRADIENTS; THREE-DIMENSIONAL CALCULATIONS