Three long-lived anticyclonic eddies in the northern South China Sea

Abstract

In August 2007, three long-lived anticyclonic eddies (ACE1, ACE2, and ACE3) were detected by both satellite sea level anomaly (SLA) map and in situ measurements in the northern South China Sea (SCS). ACE3 had a two-core (ACE3(1) and ACE3(2)) structure. In situ stations along 18°N almost cut through the centers of ACE2 and ACE3(2). Near the centers of ACE2 and ACE3(2), mean temperature and sound velocity are ∼0.657deg;C and ∼2 m s-1 larger than those in their surrounding areas, respectively, while mean salinity and density are ∼0.02 psu and ∼0.15 m3 s-1 smaller than those in their surrounding areas due to downwelling near the eddy cores. The depths of maximum and minimum salinity near the eddy cores are ∼65 m and ∼35 m larger than those in their surrounding areas. The vertical depth with current speed larger than 0.05 m s-1 can reach ∼900 m. Their detailed evolutionary processes were depicted based on the variation of geostrophic currents and the trajectories of five drifting buoys. ACE1 lasted 147 days, while ACE2 and ACE3 lasted 168 days and 210 days, respectively. ACE1 had a smaller mean SLA (18.8 cm) in its lifetime than ACE2 (21.8 cm) and ACE3 (25.3 cm) but had a larger negative mean vorticity (-7.7 × 10-6 s-1) than ACE2 (-7.0 × 10-6 s-1) and ACE3 (-7.0 × 10-6 s-1). One short-lived anticyclonic eddy that split from ACE2 and another one that merged with ACE3 both had a smaller SLA, negative vorticity, and diameter than ACE2 and ACE3, respectively. Copyright 2011 by the American Geophysical Union.