The Mode‐Water‐Induced Interannual Variation of the North Pacific Subtropical Countercurrent and the Corresponding Winter Atmospheric Anomalies
Haibo Hu, Weixuan Chen, Xiu‐Qun Yang, Yihang Zhao, Haokun Bai, Kefeng Mao
Abstract
Abstract Combining several reanalysis and in situ data sets, the low potential vorticity (PV) water masses are Lagrangian tracked in the subsurface ocean southwestwardly from the midlatitude Pacific in winter, which have significant interannual variations. The subsurface low PV water transport is proved to be closely related to the interannual variation of atmospheric North Pacific westerly jet by changing the subtropical countercurrent (STCC) and the sea surface temperature gradient adjacent. Specifically, the enhanced subsurface low PV water mass transported to the west of STCC causes strengthened northeastward warm water transport of STCC branching, and the weakened eastward branching. Therefore, significant negative temperature gradient anomalies of sea surface and lower atmosphere generate in the midlatitude to the east of 170°E. The corresponding local weakened lower atmospheric baroclinity and wave activities then lead to the convergence of anomalous downward atmospheric baroclinic Rossby waves and eventually the upper westerly jet deceleration.