Spatial Diversity of the Summer Marine Heat Waves in the South China Sea

Abstract This study reveals that the summer marine heat waves (MHWs) in the South China Sea (SCS) could be classified into two spatial types, with warming centers over the central and northern SCS (denoted as C-MHW and N-MHW), respectively. The formation of C-MHW is related to a vigorous low-level anticyclonic anomaly centered in the northern SCS. Locally, the anticyclone is accompanied with anomalous sinking motion and northeasterly anomaly over the central SCS, which enhance insolation heating and inhibit evaporative cooling associated with the southwesterly monsoon. Meanwhile, the accompanied anticyclonic wind stress anomaly and reduced wind stress induce anomalous Ekman downwelling and weaken the climatological upwelling over the central SCS, contributing to the central warming center second to the surface heat flux. From a large-scale view, the SCS anticyclone is associated with the transition from El Niño to La Niña. In summer, the SCS anticyclone is favored by the zonal SSTA gradient over the Maritime Continent to the central Pacific via triggering anomalous easterlies extending to the central SCS, by the warming around the Maritime Continent via meridional circulation and by the Indian Ocean warming via Kelvin wave response and zonal circulation. Compared with C-MHW, N-MHW results from a weaker and smaller anticyclonic anomaly associated with weaker air–sea interaction. The anticyclone favors the northern warming center mainly via insolation heating. As for the tropical SSTA, persistent warming occurs around the Maritime Continent and the Indian Ocean but with a smaller amplitude compared with C-MHW; thus, the relevant air–sea interaction processes and the resultant SCS anticyclone are weaker.