Decadal Signal in the Sea Surface Temperatures off the San\u27in Coast in the Southwestern Japan Sea

The decadal-scale variations in the southwestern Japan Sea are investigated on the basis of the offshore sea surface temperature (SST) measured by a ferryboat. The low-pass filtered SST shows alternate warm and cold periods of decadal scale, bounded by a sudden decrease and increase in 1976-1977 and 1983-1984, respectively. These temperature jumps correspond to the regime shifts that occurred in the North Pacific in the mid-1970s and late 1980s, suggesting that the Tsushima current in the Japan Sea is under the influence of the Pacific Decadal Oscillation. Similar warm and cold periods of decadal timescale are seen in the winter-mean SST variations, along with shorter-period fluctuations correlating with the winter monsoon intensity. In contrast, such a decadal variation is not observed in the summer-mean SST. This indicates that the decadal variations (and regime shifts) in the Japan Sea SST field appear clearer in winter, the same as in the North Pacific