Qiyu Song1,2, Jun Yang1*, Hang Luo1, Cheng Li3, and Shizuo Fu4,5
1Laboratory for Climate and Ocean-Atmosphere Studies, Department of Atmospheric and Oceanic Sciences, School of Physics, Peking University, Beijing, China
2Now at Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA, USA
3Department of Climate and Space Sciences and Engineering, University of Michigan, MI, USA
4Key Laboratory for Humid Subtropical Eco-Geographical Processes of the Ministry of Education, Fujian Normal University, Fuzhou, China
5School of Geographical Sciences, Fujian Normal University, Fuzhou, China
*Correspondence to: Jun Yang (E-mail: junyang@pku.edu.cn)
Abstract
Cloud is critical for planetary climate and habitability, but it is also one of the most challenging aspects of studying planets in and beyond the solar system. Here we use a cloud-resolving model (CRM) with high resolution (2 km) in a 2D configuration to simulate the clouds and circulation on tidally locked aquaplanets. We find that the substellar area is covered by deep convective clouds, the nightside is dominated by low-level clouds, and the two are linked by a global-scale Walker circulation. We further find that uniform surface warming causes the substellar cloud width to decrease, but a reduction in the day–night surface temperature contrast or an increase in the longwave radiative cooling rate causes the substellar cloud width to increase. These relationships can be roughly interpreted in accordance with simple thermodynamic theories. Comparing the results between the CRM and the global 3D general circulation model (GCM), we find that they are qualitatively consistent, including the Walker circulation, the substellar clouds, and the responses of the substellar ascending area and strength to changes in the surface temperature or in its zonal contrast. But large quantitative differences exist, such as the magnitude of the cloud water path, the cloud width, and their responses to external forcings. These results increase our confidence in using GCMs to model exoplanetary climates, although large quantitative uncertainties are always likely to exist. Future work is required to use 3D CRMs with realistic radiative transfer and the Coriolis force to examine the clouds and climates of tidally locked planets.
Key Points
1. We found a global-scale Walker circulation coupled with deep convection in the substellar area through cloud-resolving simulations.
2. The width of the convective cloud changes with surface temperature and radiative cooling.
3. Our results are qualitatively consistent with those from general circulation models, although large quantitative differences exist.
Citation
Song, Q., Yang, J., Luo, H., Li, C. and Fu, S., 2022. Idealized 2D Cloud-resolving Simulations for Tidally Locked Habitable Planets. The Astrophysical Journal, 934(2), p.149. https://doi.org/10.3847/1538-4357/ac7879
