Intrusion of the Kuroshio into the South and East China Seas.

The northward-flowing Kuroshio often intrudes westward and modulates the water masses of the South and East China Seas. These intrusions transcend multiple scales in time and space, which we demonstrate here using various independent data sets. There are two hot spots of intrusion, one in the Luzon Strait and the other off northeast Taiwan, which occur synchronously when the upstream Kuroshio weakens during winter. Beyond seasonal time scales, the two intrusions were not synchronous during 1993-2013. While intrusions into the South China Sea echoed the Pacific Decadal Oscillation, the intrusion northeast of Taiwan decreased markedly before 2002 but regularly reached the shelf thereafter. This change was due to the influence of westward impingements of cyclonic eddies from the open ocean on the Kuroshio main stream in place of anticyclonic eddies. During 1993-2001, decreasing cyclonic eddy impingements moved the Kuroshio away from northeast Taiwan, weakening the Kuroshio intrusion onto the East China Sea shelf. Thereafter, enhanced cyclonic eddy impingement during 2002-2013 weakened the Kuroshio transport, moving it closer to the shelf and enhancing its intrusion into the East China Sea.