Anomalous Relationship Between Kuroshio Transport Variability and ENSO During 1993–2020

Abstract The origin of the Kuroshio significantly modulates the variations of the Kuroshio system, playing an important role in exchanging water masses, heat, and salt between the low‐ and mid‐latitude Pacific. On the interannual time scale, it is well documented that El Niño and Southern Oscillation (ENSO) is the main factor regulating the origin of the Kuroshio, showing an anticorrelation (i.e., El Niño event relates to a weakened Kuroshio). However, while some studies have reported the decoupled variations between them, in‐depth investigations into the underlying mechanisms remain lacking. This study identifies two anomalous states where ENSO variations (leading Kuroshio variations by 10 months) decouple from the origin of the Kuroshio transport anomaly (KTA) variations, thereby elucidating the underlying mechanisms. In state 1 (S1, 1999.5–2002.10), despite an evidently negative ENSO phase, the KTA remains weakly negative (weak Kuroshio). During state 2 (S2, 2005.3–2007.12), ENSO is primarily in positive phase but accompanied by positive KTA. Based on 1.5‐layer nonlinear reduced gravity model and spice‐heave decomposition, this study suggests that the heaving process caused by mesoscale eddies results in weakly negative KTA in S1. The positive KTA in S2 is ascribed to negative wind stress curl anomalies over the northwestern Pacific (5°N–30°N, 100°E–180°E) approximately 1 year before the S2 period, and to those over the northeastern Pacific (5°N–30°N, 140°W–70°W) approximately 3 years before the S2 period. Such wind changes are likely linked to the influence from the Indian Ocean and a persistent positive ENSO phase (2002–2005), respectively.