A Numerical Model Study of "Furiwakeshio".

The "Furiwakeshio" ("Kinan Bifurcation Current"), which is caused by the Kuroshio hitting the southwestern coast of the Kii Peninsula, is studied using a high-resolution OGCM. A hindcast experiment using the OGCM is analyzed and compared with the observed data in this area. The results are summarized as follows. The mean sea level around the Kii Peninsula is characterized by a cyclonic depression in the coastal zone and the bifurcation of contours between the Kuroshio and the "Furiwakeshio" offshore of the southwestern Ku Peninsula. The OGCM with 1/18-degree horizontal resolution cannot reproduce this climatology, but can reproduce the sea' level pattern quite similar to the observed bifurcation only in a snapshot sense. The model and observations are also compared for the sea level difference between Kushimoto and Uragami, a famous index of the Kuroshio large meander. Because of the insufficiency of resolution to reproduce the tiny cape called Shiono-misaki, the model fails in reproducing observed values over 25 cm and only results in values less than 25 cm. The bifurcation patterns of current vectors and temperature contours as observed in this area in 1997 by the synoptic hydrographic surveys were not reproduced by the model in the sense of a successful hindcast. The frequency of bifurcation events through 1997 was estimated by calculating the model's westward transport along the western coast of the Kii Peninsula. The frequency of the Furiwakeshio is under-estimated by the model by about 10% when compared with the observed frequency of about 78%. Nevertheless, the lifetime and spatial structure of the Furiwakeshio once it appeared in the model are quite similar to those of the actual phenomenon. The model result shows a series of events in which the anticyclonic and cyclonic disturbances propagating on the Kuroshio 's offshore side generate a torque that changes the direction angle of the Kuroshio path between Muroto-misaki and Shiono-misaki. This is thought to be the main mechanism which causes the Furiwakeshio and is a notable feature found by the present model study.