Moist convective scaling: Insights from an idealised model

The response of clouds and moist-convective processes to heat loss to space by long-wave radiative cooling is an important feedback in the Earth's atmosphere. It is known that moist convection increases roughly in equilibrium with radiative cooling, an assumption often made in simplified models of the tropical atmosphere. In this study, we use an idealised two-dimensional model of the atmosphere introduced by Vallis et. al. and incorporate a bulk-cooling term, which is an idealisation of radiative cooling in the atmosphere. We comment briefly on the static stability of the system to dry and moist convection and characteris its moist convective response to changes in the bulk cooling. We find that, while the clear-sky regions of the model respond directly to the change in the cooling term, the regions dominated by moist convective plumes are insensitive to changes in cooling. Similar to previous findings from cloud-resolving models, we too find in our idealised setting that the majority of the increase in convection occurs via an increase in the areal coverage of convection, rather than its intensity. We argue that these small-scale convective processes are an upper bound on how quickly convective intensity can change to stay in equilibrium with radiative cooling.