Journal Article

Direct Observations of North Pacific Subsurface Low Potential Vorticity Water Impinging on the Kuroshio

Zheng, Hua, Nan, Feng, Yu, Fei, Liu, Yansong, Wang, Ran, Ren, Qiang, Zhu, Xiaohua, Zhang, Chuanzheng, Chen, Zifei, Wang, Jianfeng, Zhao, Ruixiang

2025

Overview

In this study, for the first time, we found a Subsurface Low Potential Vorticity Water (SLPVW) to the east of Taiwan Island (122°$\\mathit{{}^{\\circ}}$ –124°E^{\\circ}\\text{E}$ , 21.67°$\\mathit{{}^{\\circ}}$ –23°N$\\mathit{{}^{\\circ}}\\text{N}$ ) via an array comprising 12 current and pressure‐recording inverted echo sounders (CPIESs) from 25 June 2018 to 29 July 2019. This SLPVW exhibits remarkable intraseasonal variability, with an ∼100‐day period east of Taiwan Island, corresponding with the variability in mesoscale eddies. Compared with large‐scale climatological mean circulation, mesoscale eddy can trap SLPVW as a highway westward transport. In addition, the SLPVW impingement results in a significant subsurface velocity variation (about 10 cm/s) in the 200–400 m layer. These findings shed new light on the mechanisms of the intraseasonal variation in the Kuroshio subsurface layer. Plain Language Summary In this study, we directly observed intraseasonal variation of a Subsurface Low Potential Vorticity Water (SLPVW) in the upstream area of the Kuroshio via in‐situ measurements. This SLPVW originated from water masses from the climatological mean North Pacific Subtropical mode water (STMW) formation region. The STMW forms south of the Kuroshio Extension in the North Pacific in late winter, is an important water mass involved in shaping and memorizing climate variability in the global ocean. The SLPVW was transferred westwards over 1,300 km from the STMW formation region to the Kuroshio region by westward‐propagating mesoscale eddies. Compared with large‐scale circulation, trapping by mesoscale eddies serves as a highway for SLPVW transportation. Moreover, SLPVW impingement results in significant intraseasonal variation in the Kuroshio subsurface velocity. This study provides new insight into the dynamics of Kuroshio intraseasonal variations and highlights the importance of interactions between SLPVW and WBCs. Key Points Intraseasonal variation of Subsurface Low Potential Vorticity Water (SLPVW) was observed in the Kuroshio upstream area by a CPIES array SLPVW is trapped and transported westward by eddies from the Subtropical Mode Water climatological formation region Impingement of SLPVW plays a key role in intraseasonal variation of velocity of the Kuroshio in the subsurface layer

• Publisher: John Wiley & Sons, Inc,Wiley
• Subject: Climate variability / Climatological means / CPIES / Echo sounding / Eddies / Impingement / Intraseasonal variations / Kuroshio / Mesoscale eddies / Mesoscale phenomena / Ocean circulation / Potential vorticity / Seasonal variations / subsurface / subsurface low PV water / Subtropical climates / subtropical mode water / Variability / Variation / Velocity / Vortices / Vorticity / Water / Water masses