Interannual to interdecadal variability in the Japan Sea based on a new gridded upper water temperature dataset

A new gridded water temperature dataset of upper 400-m depths (0, 50, 100, 200, 300, and 400 m) for the Japan Sea (or East Sea) is produced by using an optimal interpolation technique from 1930 to 1996, based on oceanographic observations collected in the World Ocean Database 1998. The temperature data are analyzed by a complex empirical orthogonal function (CEOF) with six levels combined using the data for a period from 1957 to 1996, during which most of gridded data are available. Before calculating the CEOFs, low-pass or high-pass filters (cutoff period at 7 yr) are applied to separate interannual and decadal temperature changes, respectively. One interannual and two decadal CEOF modes are identified. The interannual first CEOF mode is characterized by the energetic variability around and south of the subpolar front in the western Japan Sea, accompanied by northward and northeastward phase propagations emanating from the Tsushima Strait. The decadal first CEOF mode exhibits a broad structure prevailing over the whole Japan Sea, but large amplitudes are trapped by the subpolar front, with 60°–90° phase lags between the northeastern and southwestern Japan Sea. The decadal second CEOF mode has a localized structure with strong correlations in the Yamato Basin. The relation between the atmosphere and ocean is analyzed by a correlation analysis of wintertime sea level pressures (SLPs) onto the temporal coefficients of the CEOF modes. The interannual first CEOF mode is accompanied by the SLP anomalies over the western North Pacific Ocean with steep SLP gradients over the Japan Sea, suggesting that this mode is forced by local wind anomalies associated with the SLP changes over the western North Pacific. The decadal first CEOF mode is likely to be caused by changes of the east Asian winter monsoon due to the SLP variability of the northern part of the Siberian high, which is closely associated with the decadal fluctuations of the Arctic Oscillation and the North Atlantic Oscillation. The second decadal CEOF mode is accompanied by high SLP correlations over the central North Pacific associated with strength changes of Aleutian lows, suggestive of remote forcing from the central North Pacific.