A mesoscale eddy pair southwest of Taiwan and its influence on deep circulation

Abstract

A pair of mesoscale eddies, namely, an anticyclonic eddy (AE) and a cyclonic eddy (CE), generated southwest of Taiwan was investigated using long‐term moored observations augmented with satellite and reanalysis data. AE (CE) increased the upper‐ocean current to 100 cm/s (50 cm/s) and generated temperature anomaly (T′) up to 7.5°C (−3.0°C). The vertical structure of AE presented a phase difference between T′ and velocity, with the core of T′ located south of the zero‐velocity line. This phase difference induced a −28.5 ± 12.0 TW (1 TW = 1012 W) westward eddy heat transport southwest of Taiwan. AE also presented strong nonlinearity in the upper ocean and yielded an annual mean volume transport of 0.86 ± 0.15 Sv. Energy analysis showed that both baroclinic and barotropic instabilities were important for the generation and growth of the eddy pair, and contribution from wind work was relative small. In the deep sea, AE (CE) intensified the deep currents and generated large positive (negative) T′. The deep and surface currents flowed in opposite directions during the eddy events, which is consistent with the interpretation that the eddy pair is dominated by the first baroclinic mode. The observed deep‐penetrating eddy pair could greatly influence the deep circulation of the northeastern South China Sea.