Counter-rotating eddy pair in the Luzon Strait

Abstract. Based on satellite remote sensing observation data and Hybrid Coordinate Ocean Model (HYCOM) reanalysis data, we studied the counter-rotating eddy pair in the Luzon Strait (LS). Statistical analysis revealed that when an anticyclonic mesoscale eddy (AE) (cyclonic mesoscale eddy (CE)) in the Northwest Pacific (NWP) gradually approached the east side of the LS, a CE (an AE) gradually formed on the west side of the LS, and it was defined as the AE (CE) mode of the counter-rotating eddy pair in the LS. The counter-rotating eddy pair exhibited obvious seasonal variation: the AE mode mainly occurred in the summer half of the year, while the CE mode mainly occurred in the winter half of the year. The mean durations of the AE mode and CE mode were both about 70 days. Based on energy analysis and the vorticity budget equation, the dynamic mechanism of the counter-rotating eddy pair occurrence was determined to be as follows: the AE (CE) on the east side of the LS causes a positive (negative) vorticity anomaly through horizontal velocity shear on the west side of the LS and the positive (negative) vorticity anomaly is transported westward by the zonal advection of the vorticity, finally leading to the formation of the CE (AE) on the west side of the LS.