Impingement of Subsurface Anticyclonic Eddies on the Kuroshio Mainstream East of Taiwan

Abstract

AbstractThis study shows that North Pacific subtropical mode water (STMW) characterized by low potential vorticity can approach and impinge on the Kuroshio mainstream east of Taiwan. The results of the analyses of observations and output from eddy‐resolving models show that the STMW appears with the frequency of 32.1% and 19.9% in the Kuroshio east of Taiwan. A case study with the output of the ocean general circulation model for the earth simulator during October 2015–March 2016 indicates that mode water moves southwestward toward the Kuroshio in accordance with a vertically lens‐shaped subsurface anticyclonic eddy (SAE). After the shoreward edge of the SAE impinges on the offshore edge of the Kuroshio, the northward velocity, especially subsurface velocity, of the Kuroshio increases significantly in the subsurface layer and the Kuroshio central position (KCP) extends eastward. While the SAE moves and dissipates, the offshore edge of the Kuroshio moves inshore, and then transport decreases. Both the northward velocity and the KCP changes result in the Kuroshio transport change during the impingement of SAE in the case. Statistic analysis further demonstrate that eddies those can trap moving STMW are dominated by SAEs. When SAEs encounter the Kuroshio, their subsurface northward velocity increases by 67.8% and the KCP moves eastward, and thus the northward transport of the Kuroshio increases by 43.4%.