General Circulation Model Errors Are Variable across Exoclimate Parameter Spaces
Abstract
General circulation models (GCMs) are often used to explore exoclimate parameter spaces and classify atmospheric circulation regimes. Models are tuned to give reasonable climate states for standard test cases, such as the HeldSuarez test, and then used to simulate diverse exoclimates by varying input parameters such as rotation rates, instellation, atmospheric optical properties, frictional timescales, and so on. In such studies, there is an implicit assumption that the model works reasonably well for the standard test case will be credible at all points in an arbitrarily wide parameter space. Here, we test this assumption using the opensource GCM THOR to simulate atmospheric circulation on tidally locked Earthlike planets with rotation periods of 0.1100 days. We find that the model error, as quantified by the ratio between physical and spurious numerical contributions to the angular momentum balance, is extremely variable across this range of rotation periods with some cases where numerical errors are the dominant component. Increasing model grid resolution does improve errors, but using a higherorder numerical diffusion scheme can sometimes magnify errors for finitevolume dynamical solvers. We further show that to minimize error and make the angular momentum balance more physical within our model, the surface friction timescale must be smaller than the rotational timescale.
 Publication:

The Astrophysical Journal
 Pub Date:
 December 2021
 DOI:
 10.3847/15384357/ac2d27
 arXiv:
 arXiv:2110.10925
 Bibcode:
 2021ApJ...923...39K
 Keywords:

 487;
 2020;
 1965;
 Astrophysics  Earth and Planetary Astrophysics;
 Physics  Atmospheric and Oceanic Physics
 EPrint:
 8 pages, 5 figures, accepted by ApJ