On Kuroshio front fluctuations in the East China Sea using satellite and in situ observational data

Abstract

Fluctuations of the Kuroshio front in the East China Sea and their relation to variations of the Kuroshio stream around the Tokara Strait are investigated using consecutive satellite images, sea level data, as well as water temperature records from a Japan Meteorological Agency buoy station and a ferryboat which crosses the Tokara Strait. Meanders of the Kuroshio front with typical horizontal scales of 100 to 150 km and wave periods of 14 to 20 days are found to appear ubiquitously in the East China Sea. The front meanders originate upstream over the continental slope and evolve rapidly, while propagating downstream at speeds of 20 to 26 cm s−1. Downstream southwest of Kyushu, the fully developed meanders sometimes take the form of warm filaments, and when the volume transport of the Kuroshio is large, they may develop into shed‐off warm eddies. Previous observations based on ferryboat temperature records have revealed the repeated northward migration of a clear sea surface temperature (SST) front across the Tokara Strait. It is shown that this northward migration of the SST front corresponds to the passage of the Kuroshio front meanders across the Tokara Strait, and that the unclear southward migration of the SST front is due to the presence of mixed water behind each meander. The Kuroshio front meanders in the East China Sea are further found to be closely related to the north‐southward movement of the entire Kuroshio stream in the Tokara Strait. A lag of about 10 days exists between the time the front meanders reach the Tokara Strait and the Kuroshio stream there shifts to its northernmost position.