| Path of the Kuroshio south of the Japanese islands is rather stable off the coasts of Kyushu and Shikoku, but becomes very unstable towards the Izu Islands region. Temporal variations of the Kuroshio path, estimated from coastal sea levels and motion-induced voltages in the region, do not show any preferred periodicity or any apparent correlation with variations in the atmospheric and oceanic observations at the coastal stations. Here we analyze the altimeter data (TOPEX/Poseidon) at intervals of five days for the years 1995 -99, compiled by the Oceanographic Department of the Japan Meteorological Agency, in order to investigate the reason for the change in the Kuroshio path in the Izu Island regions. The Kuroshio axis can easily be located as the place where the surface slope is steepest when crossing the current. If the Kuroshio axis moves towards the north or south, then time derivative of the sea surface height becomes very large there. For this reason we are dealt with time series of the derived sea surface height during five days rather than that of the sea surface height itself. It is found that the derived height field is generally full of meso-scale disturbances of the horizontal scale 200 - 500 km, and some of the disturbances propagate with a speed of about 5 cm/s towards the north or west or east depending on the region. Northward propagations towards the Kuroshio are most clearly seen in the Nansei Islands region and in the Izu Islands region. To the east of the Izu Islands region, clockwise rotations of the disturbances are sometimes observed. It is found that the Kuroshio path in the Izu Islands region makes a big change when a disturbance reaches there. |
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