The effects of chlorophyll-a and SST in the South China Sea area by typhoon near last decade

Based on satellite remote sensing to study the effects of ocean color and Sea Surface Temperature (SST) is the leading method at present. From 2000 to 2008, there were about 70 times storms or typhoons passed over the South China Sea Area (108-120°E, 14-24°N). In this article, authors used SeaWiFS, MODIS and serials of NOAA satellite data to statistic analysis the effects of chlorophyll-a (Chl-a) and SST in the study area caused by tropic storms and typhoons near last decade and found: firstly, the Ekman Pumping Velocity (EPV) was up-to 1.4x10^-3 m s^-1 by typhoon CHAUCHU in 2006, and was more ten times than that without typhoon. It pumped the nutrients to the euphotic zone and improved the increment of Chl-a concentration with the rate of 58.33%. and this typhoon caused the maximum decrease of SST was up to 7°C. At the same time, the average increment of Chl-a in the whole study area was about 21.13% but the decrease rate of SST was 6.36% by 16 typhoons. From the results of statistic analysis we found out that the isopycnal displacement of the seasonal thermocline explains 53% and the weight of the typhoon explains 55% of the variance of Chl-a by typhoons; In addition, the maximum amplitude of the increment of Chl-a in the study area was near to the east of Vietnam, it was up to 53%. But near the pear river estuary area with high Suspended Sand Concentration (SSC) the chl-a density decreased after typhoon and the descent rate of Chl-a was about 35%.