Localized sea surface temperature variability in the Yellow and East China Seas

The Yellow and East China Seas (YECS) are widely believed to have experienced a robust, large-scale warming trend during the last decades. However, AVHRR-based optimum interpolation sea surface temperature (SST) after removing annual cycles reveals that a long-term SST variability is characterized with a temporal pattern consisting of persistent warming by late 1990s, two SST peaks occurred at the late 1990s and mid 2000s, and weak cooling for the last decade. Spatially, a substantial warming trend downstream of the Changjian River is in contrast to weak cooling in the eastern part of the Yellow Sea. To explain this localized variability, this study adopts cyclostationary empirical orthogonal function analysis that separates principal modes with seasonally cycled loading vectors for the period of 1982−2014. Among dominant modes, the first and third modes indicate long-term changes for winter and summer respectively, while the second mode captures the interannual variability. The first mode, accounting for 25% of the total variability in the SST anomalies, appears to be associated with the meridional wind anomalies in winter. The principal component for this mode is significantly correlated with the Pacific decadal oscillation index only for the persistent warming period by late 1990s and then its correlation coefficient sharply drops to an insignificant level, implying that a potential regime shift occurred in dynamical linkage between the YECS and North Pacific circulation. The third mode likely accounts for the second peak of the mid 2000s as well as the long-term cooling trend observed near the Korea. Further investigations on a relationship between the third mode and the East Asia Summer Monsoon are current underway, and results will be presented.