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

黑潮的体积输送是根据卫星高度计获得的沿ASUKA观测线沿着的海面高度差确定的，其周期在本财政年度延长至2007年4月。该数据集已在我们的网站上发布（URL http：//www.riam.kyushu-u.ac.jp/oed/asuka/alt/index.html），随着Jason-1高度计数据的进一步发布，其周期将继续延长。在研究年际变化之前，通过比较卫星测高、Argo浮标和包括CTD和XCTD在内的水文观测的长期数据，研究观测仪器的系统趋势。同时，Argo浮标资料中可能存在由压力传感器的2-dbar阶误差引起的系统误差。利用位于黑潮沿岸和近海的反演回波测深仪（Inverted Echo Sounders，IRS）估算了9年的地转体积输送时间序列。体积输运被解释为海面高度差和等效深度的乘积，其变化的近90%可以由前者的变化来解释。这一结果支持了利用卫星测高资料估算黑潮体积输送的方法的有效性。由IES和卫星测高得到的海平面高度之间的显著差异仅在中尺度涡旋的时间尺度上存在。由卫星测高数据和表面漂移器数据联合分析得到的绝对速度场表明，四国以南的高州海山附近的弯曲发展导致黑潮向大弯曲过渡。这一转变过程也被高分辨率资料同化数值模式JCOPE的结果所证实。

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.