Regional variation of the tropical water vapor and lapse rate feedbacks

Abstract

The global and tropical mean water vapor and lapse rate radiative feedbacks are anticorrelated across contemporary climate models. Hence, despite substantial uncertainty in both, uncertainty in total clear-sky modeled radiative feedback is small compared with other sources of feedback spread. Previous work has demonstrated that no such correlation exists when grid point water vapor and lapse rate feedbacks are considered within one model. Here we show that robust physical processes nevertheless determine significant aspects of both the water vapor and particularly the lapse rate feedbacks within the tropics. The lapse rate feedback increases with surface temperature change because the tropical troposphere cannot maintain strong temperature gradients. The water vapor feedback increases weakly with surface temperature over tropical ocean but slightly decreases over land, associated with moisture availability. Water vapor feedback is more strongly related to precipitation changes, increasing most strongly in the heaviest precipitating regions and least in the weakest. Key Points Tropical lapse rate and water vapor feedbacks have robust regional structuresRegional feedback structures are explained by physical processesModel results allow a future comparison with observations