Behavior of the warm ocean water at the south coast of Kyushu

The warm ocean water filaments are emanated periodically in winter from the meandering Kuroshio Current at the East China Sea. They bring the intermittent warm ocean water intrusion into the Kagoshima Bay well known as ‘Kyucho’ phenomenon. From the satellite SST images, the warm water intrusion is also observed at the Fukiage Seashore. In addition to the warm water intrusions, the cold-water mass at the Osumi Strait is observed. In this study, the numerical analysis is performed to understand these phenomena. A density current is calculated by a multi-leveled finite difference method (FDM). Then, particle trajectories are calculated by the Lagrangian particle tracking method by using the previous current result. Particles are dealt with as passive tracers to be a model of plankton and hyponeuston (i.e. larva, eggs or seeds) of an open sea. Calculated results of the warm water mass show similar features of the SST images, i.e. the warm water intrusions into the bay and the cold-water mass generation. The warm water intrusion occurs when it reaches the mouth of the bay or the edge of the coast. The cold-water mass is concerned with a horizontal vortex shed from the edge of the cape. The cold-water mass is produced in a stagnation region by a horizontal vortex rather than upwelling from the deep ocean. The particle trajectories have a tendency to pile up in the bay and a stagnation region behind of the peninsula. These results supply the fundamental knowledge that contributes to biological problems at the south of Kyushu in winter adequately.