Variation of oceanographic conditions and sea water exchange associated with northward migration of the temperature front south of Kyushu, Japan
2009
Saito, T.(National Research Inst. of Fisheries Science, Yokohama (Japan))
As larvae and juveniles of Japanese jack mackerel, whose main spawning ground is the southern East China Sea, are transported to the waters off the southern coast of Japan by currents, they pass the Kuroshio front, south of Kyushu. With interest in the transport of larvae and juveniles, this study focused on the variation of temperature and velocity field south of Kyushu, and sea water exchange as the result. The surface temperature front off the southern coast of Kyushu is known to migrate northward repeatedly, having about a 20 day cycle. In connection with the migration of the front, formation and northeastward propagation of a warm tongue-like structure, periodic change in the sea level at Nakanoshima, and formation of the eastward current through the Ohsumi Strait have been reported. Furthermore, it has also been reported that an anticyclonic Kuroshio meander and a cyclonic eddy developed by turns on the western side of the Tokara Strait has similar cycles. Their features, however, are known only fragmentarily. We tried to describe the time evolution of the front in a three-dimensional way. By CTD (Conductivity Temperature Depth recorder) and LADCP (Lowered Acoustic Doppler Current Profiler), we carried out three-dimensional dense observations on temperature and velocity six times in the period 2000-2003. The observations were rearranged to give a sequence of temperature and velocity fields which described the evolution of the front, by using the north-south position of the front as an index. The rearrangement was justified by comparing with successive satellite images of sea surface temperature obtained in a different period.
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