The Xiamen Symposium on Marine Environmental Sciences (XMAS 2025)

The origin Kuroshio provides a vital pathway for water mass, heat, and salt exchange between the low-latitude and mid-latitude Pacific. It is well documented that El Niño and Southern Oscillation (ENSO) is the primary factor regulating the origin Kuroshio variation on the interannual timescale. Using GLORY reanalysis and AVISO satellite altimeter data, we reported two distinct anomalous states, with the origin Kuroshio transport anomaly (KTA) variation not being in concert with ENSO. Despite an evident negative ENSO phase during state 1 (S1, 1999.5~2002.10), the KTA remains weakly negative. During state 2 (S2, 2005.6~2007.5), the ENSO cycle is in a weak transition state but with a significantly positive KTA. Using barotropic dynamic decomposition and the 1.5-layer nonlinear reduced gravity model, the authors find that the relatively weak Ekman pumping driven by local wind, the joint factor of Rossby wave and the residual effects (including friction, boundary reflection, mixing, etc.), and the net surface heat flux factor can partly counteract with each other, resulting in the weakly negative KTA in S1. Furthermore, the RB factor accounts for the KTA variation and magnitude of 75% and 39%, respectively. The obvious positive KTA in S2 is ascribed to the positively anomalous net surface heat flux factor, which contributes 46% of the KTA magnitude but only 4% of the KTA variation.