Tides and short-term variabilities in the Kuroshio west of Yonakuni-jima

Direct current measurements at the mooring station M southwest of Yonakuni-jima are carried out from May 18 to June 1,1996.The observed Kuroshio Current at 290 and 594 m depths of the mooring station M is quite steady during the period of observation.The rotary spectral estimates of the current data by the maximum entropy method show that there are prominent diurnal and semidiumal spectral peaks.The semidiumal tide is predominant at 290 m depth while there is the current fluctuation with the inertial period except for the tidal oscillation at 594 m depth.There are also peaks at the period of 4-7 d.There is a significant coherence between two time series of currents at 290 and 594 m depths in the period range of 3-5 d.The Japan Meteorological Agency (JMA) wind data during the same period as the oceanic measurement are used in comparison with the current meter data.Rotary spectral estimates for the wind data show significant peaks at the period of 3-5 d.It is concluded from the cross spectra between the wind and the current that the current fluctuation of 3-5 d period at 290 m depth response to the wind fluctuation of the same periods with time lags smaller than 1 d.