Monitoring the Kuroshio in the Tokara Strait and Izu Island region by using submarine cables

Summary form only given. The Faraday´s law of electro-magnetic induction predicts that an ocean current induces a cross-stream voltage. To monitor the temporal variation of volume transport of the Kuroshio, we are measuring the voltage across the Tokara Strait since 1999 and Izu Islands since 1997 by using submarine cables. Voltages are measured at intervals of about a second, and their 10-minute averages are automatically sent via the telephone line to remote laboratories once a day. The voltages are compared with the cross-stream sea level differences, and generally good agreements are seen between the two time series. When the Kurishio hits the Miyake Island at which the sea level and voltage are observed, however, coastal sea level there becomes higher than the prediction by about 20 cm. In the Tokara Strait, the temporal variation in sea level difference leads that in voltage by about three days, suggesting that the Kuroshio Current begins to change first in the subsurface layer and then in the surface layer. Conversion factors from voltage to volume transport have been estimating by comparing the tidal component of voltage with the tidal current from a numerical model by Matsumoto et al. (2000). It is found that a volt of the voltage corresponds to a volume transport of 60 Sv for the Izu Island region, and 25 Sv for the Tokara Strait. By using these factors, the mean volume transport of the Kuroshio is estimated to be about 50 Sv at the Izu Island region, and the variation range is about 6-7 Sv at the Tokara Strait.