Generation Mechanism of the South Pacific Subtropical Dipole

AbstractDistinct pattern of interannual variability in sea surface temperature (SST) in the South Pacific [i.e., the South Pacific subtropical dipole (SPSD)] is examined using outputs from a coupled general circulation model. The SPSD appears as the second empirical orthogonal function (EOF) mode of the SST anomalies in the South Pacific and is associated with a northeast–southwest-oriented dipole of positive and negative SST anomalies in the central basin. The positive and negative SST anomaly poles start to develop during austral spring, reach their peak during austral summer, and gradually decay afterward. Close examination of mixed-layer heat balance yields that the SST anomaly poles develop mainly because warming of the mixed layer by shortwave radiation is modulated by the anomalous mixed-layer thickness. Over the positive (negative) pole, the mixed layer becomes thinner (thicker) than normal and acts to enhance (reduce) the warming of the mixed layer by climatological shortwave radiation. This thin...