Satellite Observation of Upwelling along the Western Coast of the South China Sea

Abstract

We observed the evolution of upwelling along the western coast of the South China Sea (SCS). The data we used are NOAA (National Oceanic and Atmospheric Administration) satellite AVHRR (Advanced Very High Resolution Radiometer) IR (infrared) images taken in 1996 and 1997 summer at the HRPT (High Resolution Picture Transmission) receiving station built on Tai-Ping Island, which is located in the central SCS. An upwelling intensity, defined by the total heat loss in the upwelling cold water region, is used to determine the relationship between coastal upwelling and the wind stress derived from the ERS-2 (European Remote Sensing Satellite) data. The results show that the upwelling intensity has a good linear relationship with the total alongshore wind stress while it has a low correlation with the cross-shore component of wind stress. These results imply that the alongshore wind stress is the main factor to pump the cold water up to the sea surface layer. Meanwhile, the satellite infrared images also indicate that the centroid of cold water moved southward from 15°N to 11°N during the observation period. The size of upwelling area changed as well, and finally evolved into a cold jet stretching offshore along 11°N–12°N in the mid-August 1997. Satellite infrared and altimeteric data show that the evolution of upwelling region is closely associated with the development of two anticyclonic circulations in the western SCS.