Connection Between the Enhancement of Tropical Precipitation and Subtropical Land Drying Under Climate Change

Abstract:

The changes in precipitation and circulation due to greenhouse gas (GHG) forcing are usually described in two different scales: a fast response to direct radiative forcing and a slow response to the mean surface warming. Previous studies have shown that the drying over subtropical Mediterranean-like lands (i.e. California, Chile, and the Mediterranean) and tropical lands form during fast response period and last through the slow response. Mechanisms including direct GHG forcing, land-sea contrast and time evolution of SST pattern have been proposed to explain these patterns. However, there is no clear census whether the changes in tropical precipitation is connected to the subtropical land drying. In this research, we assume that the diabatic heating released by the monsoonal-like tropical precipitation anomalies interact with the subtropical anticyclones through the propagation of the Rossby wave. The Rossby wave then interact with midlatitude westerlies and modulate the subtropical anticyclones. We test our hypothesis through a set of fully coupled large ensemble experiment in CESM2 and an idealized dry model. The idealized dry model follows the full set of primitive equations of the atmosphere in a spherical coordinate system and no mass changes of atmosphere due to precipitation are included. We first run CESM2 under abrupt 4xCO2 forcing scenario and take out the diabatic heating released over tropical land precipitation anomalies. We then prescribe this diabatic heating onto the idealized dry model. We expect a precipitation decline over the Mediterranean-like lands.