Convection and Clouds under Different Planetary Gravities Simulated by a Small-domain Cloud-resolving Model

TL;DR

This study uses a cloud-resolving model to explore how planetary gravity affects convection, cloud formation, and climate stability, revealing that lower gravity leads to increased water vapor, cloudiness, and different convective regimes.

Contribution

It demonstrates the impact of planetary gravity on convection states, cloud properties, and radiative effects using high-resolution simulations in a small-domain model.

Findings

Lower gravity increases sea surface temperature and cloudiness.

Convection transitions from steady to oscillatory with increased stellar flux.

High-level clouds obscure atmospheric CO2 features in oscillatory convection.

Abstract

In this study, we employ a cloud-resolving model (CRM) to investigate how gravity influences convection and clouds in a small-domain (96 km by 96 km) radiative-convective equilibrium (RCE). Our experiments are performed with a horizontal grid spacing of 1 km, which can resolve large (> 1 km$^2$) convective cells. We find that under a given stellar flux, sea surface temperature increases with decreasing gravity. This is because a lower-gravity planet has larger water vapor content and more clouds, resulting in a larger clear-sky greenhouse effect and a stronger cloud warming effect in the small domain. By increasing stellar flux under different gravity values, we find that the convection shifts from a quasi-steady state to an oscillatory state. In the oscillatory state, there are convection cycles with a period of several days, comprised of a short wet phase with intense surface precipitation and a dry phase with no surface precipitation. When convection shifts to the oscillatory state, water vapor content and high-level cloud fraction increase substantially, resulting in rapid warming. After the transition to the oscillatory state, the cloud net positive radiative effect decreases with increasing stellar flux, which indicates a stabilizing climate effect. In the quasi-steady state, the atmospheric absorption features of CO$_2$ are more detectable on lower-gravity planets because of their larger atmospheric heights. While in the oscillatory state, the high-level clouds mute almost all the absorption features, making the atmospheric components hard to be characterized.