Title:Volume and Transport of Eddy-trapped Mode Water South of the Kuroshio Extension

Journal: Journal of Geophysical Research: Oceans, in press

Authors:SHI F., Y. -Y. Luo*, and L. -X. Xu

Abstract: Mesoscale eddies play an important role in transporting North Pacific subtropical mode water (STMW). Using eddy samples adopted from a 3‐day and 0.1° ocean model output spanning from 1980 to 2014, this study quantifies the eddy‐trapped STMW volume and transport south of the Kuroshio Extension. Based on the shape of their isopycnals, anticyclonic eddies (AEs) in the region are classified into two types. The first type (AE1) has a lens‐like structure of isopycnals, and the second type (AE2) has downward bending isopycnals throughout the pycnocline. In contrast to AE2, a cyclonic eddy is characterized by upward bending isopycnals throughout the pycnocline. Although all three eddy types can trap STMW, the low potential vorticity water within an AE1 is found to be thicker in the spring and better preserved through the rest of the year. A quantitative estimation finds that the STMW volume trapped by an AE1 is approximately 1.5 and 2.5 times larger than the volumes trapped by an AE2 and a cyclonic eddy, respectively. The eddy‐trapped STMW moves primarily westward, with its meridional integration between 25 and 35°N reaching ~1 Sv at 143°E, approximately 17% of the time‐mean total zonal STMW transport there. This study highlights the important role of eddies (particularly the AE1) in carrying STMW westward and thus modulating North Pacific climate variability.