A satellite and field view of the winter SST variability in the Taiwan Strait

Satellite-sensed advanced very high resolution radiometer (AVHRR) sea surface temperature (SST) data over eight winters (1996-2003) and shipboard measurement during winter 2002 were used to analyze the winter SST patterns of variability in the middle of Taiwan Strait. Empirical orthogonal function (EOF) analysis of the spatial and temporal variance for 81 nearly cloud-free quarter monthly images was performed. The time series of spatial mean SST was like a non-linear mode associated with the seasonal thermal variation, having an average value about 20°C. The EOF analysis shows that the variance of oceanic feature was more significant in space than in time. The first mode (85.7%) of the spatial variance shows a persistent front near the Chang-Yuen Ridge in the middle of Taiwan Strait, which separates warmer surface water (>22°C) to the southeast from the colder waters (<19°C) off Mainland China to the northwest. The maximum temperature and salinity gradient at Chang-Yuen Ridge were found about 0.11°C/km and 0.048 psu/km, respectively. The second and third spatial variance modes are extremely low energy about 3.13% and 1.92%, respectively. The EOF's signal and field observation revealed that the heating exchange, balance and its strength (i.e. coolness index) of cold water to warm water, were temporally shifted in winter. From these images, we also constructed an overall coolness index, which revealed the relative strength of Mainland China Coastal Current in relation to the interaction of the South China Sea Warm Current and Kuroshlo Counter Current.