Cloud behaviour on tidally locked rocky planets from global high-resolution modelling

Determining the behaviour of convection and clouds is one of the biggest challenges in our understanding of exoplanetary climates. Given the lack of in situ observations, one of the most preferable approaches is to use cloud-resolving or cloud-permitting models (CPM). Here we present CPM simulations in a quasi-global domain with high spatial resolution (4 × 4 km2 grid) and explicit convection to study the cloud regime of 1:1 tidally locked rocky planets orbiting around low-mass stars. We show that the substellar region is covered by deep convective clouds and cloud albedo increases with increasing stellar flux. The CPM produces relatively lower cloud liquid water concentration, smaller cloud coverage, lower cloud albedo and deeper H2O spectral features than previous general circulation model simulations using empirical convection and cloud parameterizations. Furthermore, cloud streets—long bands of low-level clouds oriented nearly parallel to the direction of the mean boundary-layer winds—appear in the CPM and substantially affect energy balance and surface precipitation at a local level.