Seasonal cycle of marine heatwaves in the northern South China Sea

The seasonal properties and heat budget of marine heatwaves (MHWs) on the northern South China Sea (SCS) continental shelf are investigated. The winter MHWs are generally the warmest, gradually weakening in the following seasons. In winter and spring, all events have a temperature elevated by more than 1 degrees C while approximately half of the MHWs in summer and fall have temperatures elevated by less than 1 degrees C. The MHW duration is longest in winter, second longest in fall, and shortest in spring. Three types of MHWs have been defined based on the main heat source; i.e., air-sea heat flux dominant, ocean advection dominant, and mixed types. Air-sea heat flux is the dominant source for more than 80% of MHWs in winter and fall, similar to 70% of MHWs in spring, and similar to 50% in summer. There are slightly more ocean advection dominant events than Mixed-MHWs. Ocean advection always weakens an air-sea heat flux dominant MHW and enhances other types of events, so that the net heat supply is smallest for air-sea heat flux dominant MHW types. Ocean advection is mainly modulated by cross-slope water exchanges along the continental shelf edge. The offshore (onshore) cross-slope flow induces a negative (positive) contribution to MHW development. These results provide new insight into the seasonal cycle of MHWs on the northern SCS continental shelf.