A statistical study on the subthermocline submesoscale eddies in the northwestern Pacific Ocean based on Argo data

Abstract

AbstractIn this study, statistical characteristics and spatiotemporal variability of the cold‐core subthermocline eddies (STEs) discovered by Zhang et al. (2015) in the northwestern Pacific are investigated with 14 years of Argo temperature/salinity (T/S) data between 2002 and 2015. By applying an objective identification procedure to Argo T/S profiles, a total of 337 lens‐like STEs that trap cold and fresh homogeneous water are obtained. The STEs' cores are primarily located between 26.5 and 26.9 (300–800 m) and their shapes share a uniform Gaussian structure in vertical. Vertical and horizontal scale of the STEs is generally between 100 and 200 m and 5 and 15 km, respectively, suggesting that they are in the category of submesoscale processes. According to their different densities and seasonalities, the STEs are classified into upper and lower types with density interface of 26.7 . The number of upper‐type STEs is much larger in spring and summer than in autumn and winter while that of lower‐type ones show relatively uniform seasonal distributions. Spatially, the STEs are primarily distributed within the region between the Kuroshio Extension (KE) and subarctic front (SAF) in meridional and 140°E–155°E in zonal direction. Based on STEs' spatial distributions and vertical locations, we propose to name these STEs as KE intermediate‐layer eddies (Kiddies). Water property analysis suggests that the Kiddies most likely originated from the SAF region. For the upper‐type Kiddies, they are probably generated through subduction associated with mixed‐layer frontogenesis, which at least contribute to 0.25 Sv annual subduction rate for the layers 26.2–26.7 .