Interannual variations of the volume transport and path of the Kuroshio south of Japan

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Volume transport of the Kuroshio has been determined from sea surface height difference along the ASUKA observation line obtained by satellite altimeters, and its period is extended to April 2007 in this fiscal year. The dataset has been released at our web site (URL http://www.riam.kyushu-u.ac.jp/oed/asuka/alt/index.html), and its period will continue to be extended as any further release of Jason-1 altimeter dataPrior to studying interannual variations, systematic trends of observation instruments are investigated by comparing long-term data of satellite altimetry, Argo floats and hydrographic observations including both CTD and XCTD. The altimetry data and the hydrographic observations are confirmed to agree well Meanwhile, a systematic error induced by a possible 2-dbar-order error in the pressure sensor is suggested to exist in the Argo floats data.Nine-year time series of the geostrophic volume transport referred to a 1000 dbar surface has been estimated using Inverted Echo Sounders (IRS) located at both coastal and offshore sides of the Kuroshio. The volume transport is then interpreted as the products of the sea surface height difference and the equivalent depth, and nearly 90% of their variations are explained by variations of the former. This result supports efficiency of the method to estimate the Kuroshio volume transport using satellite altimetry data. Note that significant differences between the sea surface height determined by the IES and one from the satellite altimetry are found only at the time scale of mesoscale eddies.Absolute velocity field determined by combined analysis of satellite altimetry data and surface drifter data has revealed that development of a meander adjacent to the Koshu seamount south of Shikoku leads to transition to a large meander of the Kuroshio. This transition process is also confirmed in results of a high-resolution data-assimilated numerical model, JCOPE.