A cloud‐resolving modeling study of cloud radiative effects on tropical equilibrium states

Abstract

The radiative effects of water and ice clouds on tropical equilibrium states are investigated based on four two‐dimensional cloud‐resolving simulations imposed by a zero vertical velocity and constant zonal wind and sea surface temperature (SST). The model is integrated for 40 d to reach equilibrium states. Experiment CRFWI includes radiative effects of both water and ice clouds whereas experiment CRF00 excludes them. Experiments CRF0I and CRFW0 are identical to CRFWI except the radiative effects of water and ice clouds are excluded, respectively. CRF00 and CRFW0 produce similar cold and dry equilibrium states whereas CRFWI and CRF0I generate similar warm and humid equilibrium states. This indicates that water clouds may not have radiative effects on equilibrium states. The experiments without ice radiative effects (CRFW0 and CRF00) emit more IR radiation into space than the experiments with ice radiative effects (CRFWI and CRF0I) do. Colder air by more IR emission strengthens air‐sea flux exchanges and lowers air capacity to hold water vapor, resulting in larger surface evaporation and drier atmosphere. An increased surface evaporation is balanced with a stronger surface rain rate in the equilibrium domain mean water balance.