Responses of cold eddies to Typhoon Soulik (2013) off northeastern Taiwan Island

Abstract

By using multisource reanalysis datasets, satellite data, etc., the influences of Typhoon Soulik on the upper ocean of two cold eddies off northeastern Taiwan Island (hereafter referred to as the P-Cold Eddy and D-Cold Eddy), which are distributed around Pengjia Islet and northeastern Diaoyu Island, respectively, were investigated. The results showed that the P-Cold Eddy was strengthened, and the D-Cold Eddy, which was previously invisible in the surface layer, began to appear. The seawater temperatures in the upper mixed layer of the two cold eddies decreased the most on 13 July, with the sea surface temperatures (SSTs) decreasing by 1.16 °C and 0.97 °C and the mixed layer temperatures decreasing by 1.23 °C and 1.06 °C, respectively. The upper ocean cooling of the P-Cold Eddy was mainly caused by upwelling, whose formation was related to the climb of more Kuroshio subsurface cold water northward forced by the typhoon. The upwelling of the D-Cold Eddy was weak, and the warming effect of the heat pump could be observed at the bottom of its mixed layer. The process of cooling and increasing salinity in the mixed layer of the D-Cold Eddy was mainly associated with the inflow of the upper cooler and saltier seawater from the P-Cold Eddy. The air–sea exchange term was not the main factor in the cooling of the seawater in the mixed layer during the forced stage, but it became dominant during the relaxation stage, and the latent heat flux (Q_LH) contributed significantly to its change.