Interannual variability of the Kuroshio onshore intrusion along the East China Sea shelf break: Effect of the Kuroshio volume transport

The interannual variability of the Kuroshio onshore intrusion (KOI) across the East China Sea (ECS) shelf break and its response to the ECS Kuroshio volume transport (KVT) during 1993 approximate to 2010 are studied based on a high-resolution, real-time, and global ocean general circulation model. Since variability of KVT is mainly determined in the interior Pacific, it is rather a remote than a local factor for the local ECS KOI. On interannual time scales, KVT affects KOI not only in the net volume transport across the entire shelf break but also in the spatial pattern along the shelf break. When KVT increases, the intrusion decreases (increases) upstream (downstream) of the major intrusion region northeast of Taiwan, the retreating increases (decreases) upstream (downstream) of the main veering region southwest of Kyushu. These patterns are caused by cyclonic eddies induced by the seaward deflection of the Kuroshio axis from the shelf break, which ultimately results from the KVT increase. A diagnostic mechanism of KOI approximate to Msin?()|delta h-1| is proposed, where h is the bottom depth, is the angle between isobaths and the vertically averaged current, and M is the absolute volume transport at the shelf break. is large in the major intrusion/retreating regions and stable on interannual time scales while M changes with opposite signs between upstream and downstream of the major intrusion/retreating regions. The mechanism explains well the relation of local KVT and the spatial pattern of KOI along the shelf break, in both the mean state and the interannual variations.