Recent surface cooling in the Yellow and East China Seas in association with the North Pacific climate regime shift in 1997/98

Abstract

The Yellow and East China Seas (YECS) have warmed during the last decades. In addition to this warming trend, the sea surface temperature (SST) reveals a basin-scale surface cooling trend after the late 1990s. In this study, we investigated the characteristics of this recent cooling trend and its dynamic relationship with large-scale climate variability through cyclostationary ortho-gonal function analysis for the 1982&#8211 2014 period. Both regressed surface winds on the primary mode of the YECS SST and trends in air-sea heat fluxes show that the intensification of the northerly winds in winter contribute largely to the recent cooling trend by increasing heat loss to the atmosphere. As a localized oceanic response to these winds, the upwind flow seems to bring warm waters and partially counteracts the basin-scale cooling, thus contributing to a weakening of the cooling trend along the central trough of the Yellow Sea. In the context of the large-scale climate variabilities, a strong relationship between the YECS SST variability and Pacific Decadal Oscillation (PDO) has considerably weakened during the recent cooling period after the late 1990s as the PDO signals appeared to be confined within the eastern basin of the North Pacific in association with the regime shift. In addition to this decoupling of the YECS SST from the PDO, the intensified Siberian High pressure system likely enhanced northerly winds, leading t the characteristics of this recent cooling trend and its dynamic relationship with large-scale climate variability through cyclostationary ortho-gonal function analysis for the 1982&#8211 2014 period. Both regressed surface winds on the primary mode of the YECS SST and trends in air-sea heat fluxes show that the intensification of the northerly winds in winter contribute largely to the recent cooling trend by increasing heat loss to the atmosphere. As a localized oceanic response to these winds, the upwind flow seems to bring warm waters and partially counteracts the basin-scale cooling, thus contributing to a weakening of the cooling trend along the central trough of the Yellow Sea. In the context of the large-scale climate variabilities, a strong relationship between the YECS SST variability and Pacific Decadal Oscillation (PDO) has considerably weakened during the recent cooling period after the late 1990s as the PDO signals appeared to be confined within the eastern basin of the North Pacific in association with the regime shift. In addition to this decoupling of the YECS SST from the PDO, the intensified Siberian High pressure system likely enhanced northerly winds, leading t