Investigating the impacts of atmospheric heating on rainfall distribution and boundary-layer energy balance with a cloud-resolving model

Relying on convective parameterizations, coarse-resolution global climate models cannot explicitly resolve tropical precipitation intensity distribution, and possible changes caused by forcings. We use a cloud-resolving model to study how imposed atmospheric radiative heating (such as that caused by greenhouse gases or absorbing aerosols) may alter precipitation intensity in a radiative-convective equilibrium setting. It is found that the decrease in total precipitation is realized through reducing relatively weak (<400 mm/ day) events. In contrast, the fraction generated by more intense events almost doubles. This behavior occurs because free-tropospheric heating decreases surface latent heat flux by increasing boundary layer humidity, which tends to enhance more intense events. A boundary layer energy budget analysis suggests that free-tropospheric heating raises boundary layer temperatures mainly through a reduction in rain re-evaporation. This insight leads to a predictive theory for the surface sensible and latent flux changes. Furthermore, turning off rain re-evaporation is very effective at inducing convective organization, which takes place despite the simultaneous inclusion of multiple factors known to inhibit organization. The results help understand how cloud processes shape the temperature and precipitation responses to atmospheric heating.