Interannual variability of summer coastal upwelling in the Taiwan Strait

This study dealt with the interannual variability of summer coastal upwelling in the Taiwan Strait, based on empirical orthogonal function (EOF) analysis. Three datasets were used for the analysis: the National Oceanic and Atmospheric Administration (NOAA), Advanced Very High Resolution Radiometer (AVHRR) sea surface temperature dataset from 1985 to 2005; hydrographic records at two coastal stations from 1970 to 2001; and cruise measurements in 1988 and 2004. The results indicated that the first mode (85.3%) of the spatial variance showed a persistent front, which was generally aligned northeast–southwestward in the western Taiwan Strait. This front separated colder water on the west side from warmer water on the east side. The eigenvector time series showed that the variability of this front with time was closely correlated with the change in the wind stress anomaly of the alongshore wind component, derived from 17 years of the European remote sensing (ERS) satellite and QuickScat wind dataset from 1992 to 2005. Records of water temperature and salinity anomaly at Pingtan Island (Is.) located in the northwestern Taiwan Strait, and Dongshan Is. located in the southwestern Taiwan Strait, showed that a negative temperature anomaly appeared along with a positive salinity anomaly in some years. This suggested a dominant influence of cold and saline upwelling water at the surface. The years of notable cooling events derived from the station measurements were generally consistent with the time series of the EOF Mode 1. The change in upwelling derived from cruise measurements further confirmed the change shown by the EOF Mode 1 time series. These 1985–2005 results indicated that for the entire western Taiwan Strait summer coastal upwelling was strong in 1987, 1993, and 1998, and that upwelling in the northwest and the southwest Taiwan Strait showed different behavior. A delayed ENSO (El Niño Southern Oscillation) effect was suggested as a major mechanism for the interannual variability of Taiwan Strait coastal upwelling.