The contributions of deep and shallow convection to tropical precipitation interannual variability and its changes under global warming

Tropical precipitation is closely related to surface convergence (SC) and sea surface temperature (SST). Previous studies led to the development of a simplified two-mode model to explain the climatological pattern of tropical precipitation, which decomposes tropical precipitation into two components: one driven by shallow convection and the other by deep convection. However, the original model shows limitations in accurately describing the pattern of tropical precipitation interannual variability (TPIV) and its changes under global warming. The present study revises the two-mode model by introducing spatially varying coefficients of shallow and deep convection. These modified models show improved performance in approximating TPIV and its changes compared to the original version. The revised two-mode models further reveal that the connection between the deep convection component of TPIV and SST is spatially varying, characterized by the differing impact of SC on deep convection under various background SST conditions. In contrast, the shallow convection component of TPIV is primarily related to SC, and their spatial relationship is almost constant. Moreover, deep convection dominates TPIV in the warm pool region, whereas the contributions of deep and shallow convection to TPIV are comparable in the eastern Pacific convergence zone. Under global warming, deep convection dominates the amplification of precipitation interannual variability over the equatorial central-eastern Pacific, resulting from both enhanced atmospheric instability and stronger sensitivity of deep convection to surface convergence.