This study reveals that the summer marine heatwaves (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 associated with strong large-scale tropical air-sea interaction. Locally, the anticyclone is accompanied with anomalous subsiding and northeasterly over the central SCS, which enhance the insolation heating and inhibit the evaporative cooling associated with southwesterly monsoon. Meanwhile, the anticyclonic wind stress anomaly and reduced wind stress cause anomalous Ekman downwelling and weakens 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 Nino to La Nina. In summer, the prominent zonal SSTA gradient over the Maritime Continent to central Pacific and the warming around the Maritime Continent and Indian Ocean could favor the SCS anticyclone, via triggering anomalous easterly, meridional circulation, 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, while other local processes make negative or insignificant contribution. As for the tropical SSTA, persistent warming occurs around the Maritime Continent and Indian Ocean but with smaller amplitude compared with C-MHW, thus the relevant air-sea interaction processes and resultant SCS anticyclone are weaker.

Marine heatwaves