10–30-day moist static energy evolutions related to the persistent heavy rainfall event in different stages of flood season over South China

Abstract

In this study, the flood season in South China (SC) was divided into three stages: two first rainy seasons (FRSs) around the South China Sea summer monsoon onset and one second rainy season when Typhoon prevails, denoted as FRS1, FRS2, and SRS, respectively, and then we diagnosed the moist static energy (MSE) budget associated with the 10–30-day persistent heavy rainfall (PHR) over SC during these periods. The results indicate that there are great differences in the recharge of PHR-related MSE in different stages of the flood season in SC: The FRS1 MSE associated with PHR moves southeastward from midlatitude; the large MSE is maintained in SC during the FRS2; during the SRS, the MSE perturbation propagates from the tropical western North Pacific to SC. From the perspective of the local MSE budget in SC, meridional and zonal advection play a key role in the maximum MSE change in the FRS1; the FRS2 and SRS MSE tendency is mainly determined by zonal advection and meridional advection, respectively. In contrast, the 10–30-day propagating perturbation of MSE changes during both the FRS1 and FRS2 are mainly affected by the zonal advection, while the meridional circulation is dominant in the SRS. The cumulative contribution of external forcing (including radiation and surface heat fluxes) during the SRS to the propagation of PHR-related MSE perturbation can reach more than 30%, and the closer to the land, the stronger the external forcing. During the FRS (including FRS1 and FRS2), however, the external forcing contributes little, even negatively.