This study deals with the interannual variation of summer upwelling in the Taiwan Strait (TS), based on the empirical
orthogonal function analysis. NOAA AVHRR sea surface temperature dataset from 1985-2005 and hydrographic records
at two coastal stations from 1970-2001 are used. The results indicate that the first mode (85.3%) of the spatial variance
shows a persistent front, which is generally aligned northeast-southwestward in the western TS. The eigenvector time
series show that the variability of this front with time is closely correlated with the change in the wind stress anomaly of
alongshore wind component derived from 17 years of ERS and QuickSCAT wind dataset from 1992-2005. The records
of the water temperature and salinity anomaly at Pingtan Is. located in the northwestern TS, and Dongshan Is. located in
the southwestern TS show that a negative temperature anomaly appears along with a positive salinity anomaly in some
years. This suggests a dominant influence of cold and saline upwelling water at the surface. The years for notable
cooling events derived from the station measurements are generally consistent with the time series of EOF Mode 1.
These results indicate that for the entire west TS, the summer coastal upwelling was strong in 1987, 1993, and 1998
during the period from 1985 to 2005. A delayed ENSO effect is suggested as a major mechanism for the interannual
variability of TS coastal upwelling.
SeaWiFS SeaWiFS Chl and AVHRR SST time-series in August, 1998 were used to evaluate short-term variability of Chl associated with upwelling events in the western Taiwan Strait. Extents of eutrophic waters (SeaWiFS Chlorophyll > 1mg/m3) and extents of colder than non-upwelling waters were calculated for the western strait and for the north and south portions, respectively. High extents of eutrophic waters were always accompanied by high extents of colder than nonupwelling waters, indicative of tight coupling of Chl with SST evolution and thus with upwelling activities. Only one-day lag of phytoplankton growth to upwelling was detected. The temporal patterns of upwelling events were found different in the northwestern and southwestern Taiwan Strait. In the north portion, a short relaxation of upwelling probably occurred between early and mid-August. One unique strong upwelling event was likely going from early through mid-August, peaking before Aug. 13th in the south portion. It resulted in chlorophyll enhancement developing and reaching peaks not concurrently in these two upwelling zones. The duration of one upwelling event in the western Taiwan Strait in August was estimated to be ca. 12 days. Two distinctive upwelling systems located in the northwestern and southwestern Taiwan Strait were further inferred.