The role of cloud radiative heating in determining the location of the ITCZ in aqua planet simulations

Abstract:

We investigate the relationship between the tropical circulation and cloud radiative effect. We use output from the Clouds On Off Klimate Intercomparison Experiment (COOKIE) to test the hypothesis that local cloud radiative heating pulls convection equatorward (where sea surface temperatures are at a maximum). In aqua planet simulations with a fixed SST pattern, the cloud radiative effect leads to an equatorward shift of the Intertropical Convergence Zone (ITCZ). Additionally, cloud-radiation interactions strengthen the mean meridional circulation and consequently enhance the moisture convergence. Precipitation peaks at higher values in a narrower band when the cloud radiative effects are active, compared to when they are inactive, due to the enhancement in moisture convergence. We show that the cloud radiative heating in the upper troposphere increases the temperature, weakens CAPE, and inhibits the onset of convection until it is closer to the equator, where SSTs are higher. Cloud radiative heating reduces the total precipitation across the tropics while it enhances cloud water path (liquid plus ice), which suggests that the cloud radiative heating reduces precipitation efficiency in these models.