Regional Characteristics of Cloud Radiative Effects before and after the South China Sea Summer Monsoon Onset


  • The South China Sea summer monsoon (SCSSM) onset is characterized by rapid thermodynamical changes in the atmosphere that are critical to regional weather and climate processes. So far, few studies have focused on the changes in the associated cloud and radiative features. This study investigates spatiotemporal characteristics of top-of-atmosphere (TOA) cloud radiative effects (CREs) before and after the SCSSM onset over the South China Sea (SCS) and South China (SC), based on the 2001–2016 Clouds and the Earth’s Radiant Energy System (CERES) Energy Balanced and Filled (EBAF) satellite data and ERA-Interim reanalysis data. Before the SCSSM onset, strong net CRE (NCRE) dominated by its cooling shortwave component occurs over SC, while descending motion and weak NCRE prevail over the SCS. In the SCSSM onset pentad, convection, high clouds, and longwave and shortwave CREs (LWCRE and SWCRE) abruptly increase over the southern and central SCS, and their high-value centers subsequently move northeastward and are strongly affected by the western Pacific subtropical high. The strong offset between LWCRE and SWCRE enables the NCRE intensity (TOA radiation budget) to be quite small (large) between the SCS and the western North Pacific after the SCSSM onset. In contrast, low–middle-level clouds and strong cooling SWCRE remain over SC after the SCSSM onset, but the increasing high clouds and LWCRE weaken (intensify) the regional NCRE (TOA radiation budget) intensity. These marked latitudinal differences in CREs between the SCS and SC primarily arise from their respective dominant cloud types and circulation conditions, which manifest the differences between the tropical SCSSM and subtropical East Asian monsoon processes. The results indicate that regional cloud fractions and CREs before and after the SCSSM onset are strongly modulated by quickly changed large-scale circulation over the East Asian monsoon regions, and the spatiotemporal variation of CREs is a response to the monsoonal circulation adjustment to a large extent.
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