Ocean thermodynamics behind the asymmetry of interannual variation of South China Sea winter cold tongue strength

During the boreal winter over the South China Sea (SCS), an elongated pool of cool sea surface temperatures (SSTs), known as the cold tongue region (CTR), exists. This paper examines the ocean thermodynamics behind the asymmetry in CTR interannual SST anomaly between strong and weak CTR events observed during November–December (ND) and January–February (JF) for 1982–2015. Generally, weak CTR events are more dominant than strong CTR events in terms of SST anomaly magnitude and spatial extent. Over the northern and southern halves of northern CTR, the key processes regulating the interannual ND CTR strength are the surface heat flux and horizontal advection, respectively. During JF, the surface heat flux mainly regulates the entire northern CTR. Over the southern CTR, the key processes controlling the ND strength are the surface heat flux and horizontal advection, while only the horizontal advection controls the JF strength. For the periods and regions where the surface heat flux is the dominant thermal process, considering the mixed layer depth effect, the latent heat flux in most cases is the most important component.