Sea Surface Variability of Upwelling Area Northwest of Luzon, Philippines

Abstract

The upwelling events during winter at the northwest tip of Luzon are among the sea surface features occurring in the South China Sea. The variability of sea surface in the upwelling area was determined using 9-year satellite altimeter data from TOPEX/ Poseidon and ERS 1 & 2. Using Empirical Orthogonal Function (EOF) decomposition the variability of the area was resolved. Two modes were derived representing the sea level anomaly variations of the upwelling area that peak during the monsoon periods. The sea level anomaly associated with the upwelling event coincided with the positive wind stress curl, which has been suggested to be due to the topographic steering of the wind that can be initiated by the northeast wind at the tip of Luzon. ENSO events also appear to modulate the timing of the development and decay of upwelling in the northwest of Luzon. El Niño events initiate early development while La Nina episodes delay the occurrence of upwelling events in the area. The intensity or strength of El Niño and La Niña episodes seems to influence the extent/ magnitude of the upwelling area.