Interannual variability of the South China Sea associated with El Niño

Interannual sea surface temperature (SST) anomalies in the South China Sea (SCS) are largely influenced by El Niño through El Niño–driven atmospheric and oceanic changes. This paper discovers a new observed feature of the SCS SST anomalies: a double‐peak evolution following an El Niño event. The first and second peaks occur around February and August, respectively, in the subsequent year of the El Niño year (denoted by February [+1] and August [+1]). During and after the mature phase of El Niño, a change of atmospheric circulation alters the local SCS near‐surface air temperature, humidity, cloudiness, and monsoon wind. These factors influence surface heat fluxes and oceanic flows over the SCS that can either warm or cool the SCS depending upon stages of SST anomaly evolution. The shortwave radiation and latent heat flux anomalies are major contributions to the first peak of the SCS SST anomalies, although the geostrophic heat advections warm the western boundary region of the SCS. After the first peak of February [+1], both the Ekman and geostrophic heat advections, assisted with a reduction of the net heat flux anomalies, cool the SCS SST anomalies. In August [+1], the mean meridional geostrophic heat advection makes the SCS SST anomalies peak again. Then, the latent heat flux anomalies (mainly attributed to anomalous air‐sea difference in specific humidity) and the mean zonal geostrophic heat advection take over for the cooling of the SCS after the second peak.