Seasonal variability of the Kuroshio Current at the PN Section in the East China Sea based on in-situ observation from 1987 to 2010

Abstract

As the spatio-temporal variability of the Kuroshio is highly influenced by mesoscale eddies, representing its seasonal variability characteristics requires sufficiently long term observations to reduce the uncertainties. Geostrophic velocity data estimated from hydrographic observation from 1987 to 2010 and the shipboard ADCP velocity data from 1993 to 2008 at the PN Section in the central East China Sea are collected to view the seasonal variability objectively. From both types of observation, it is found that the seasonal climatology mean of the Kuroshio Current exhibits significant difference in three areas, which are located at the Kuroshio Current core and its two flanks in a shallow layer less than 300 m, with the weakest northeast current at the core in autumn, the strongest counter current on the right flank in spring, and the strongest northeast current on the left flank in autumn, respectively. The seasonal variance of the Kuroshio Current also exhibits significant difference on the offshore side of the Kuroshio, with larger variance in spring and summer while smaller variance in autumn and winter. For the current parallel to the PN Section, the ratio of the seasonal variability component to the intraseasonal variability component is relatively smaller than that for the current perpendicular to the PN Section. Further analyses indicate that the seasonal variability at the PN Section is tightly linked to the upstream and downstream current variability.