The flow pattern north of Taiwan and the migration of the Kuroshio

Abstract

The migration of the Kuroshio and mesoscale flow pattern north of Taiwan were studied using the historical ship-board acoustic Doppler current profiler (Sb-ADCP) current velocity and hydrographic measurements, moored current velocity, water temperature and salinity time series, snapshot current velocity observations and infrared images. The Kuroshio migrated both seasonally and intra-seasonally, with the former being more pronounced. The flow pattern north of Taiwan was significantly impacted by the seasonal migration of the Kuroshio. In summer the Kuroshio generally moved away from the shelf, colliding with the zonally running shelf breaks of the East China Sea (ECS) and splitting into an eastward mainstream and a northwestward branch current. Southwest of the branch current, a counterclockwise circulation was found along the edge of the shelf northeast of Taiwan, through which the subsurface Kuroshio water intruded forming a cold dome. In winter the Kuroshio moved close to and sometimes onto the northern shelf of Taiwan. The intrusion of the Kuroshio dominated the flow pattern in the region, causing the disappearance or obscuration of the counterclockwise circulation and cold dome. A sharp horizontal temperature front accompanying the horizontal velocity front was found on the northern shelf of Taiwan, through which the current flowed mainly northward against the winter monsoon. Intra-seasonal variations in flow patterns north of Taiwan and the intra-seasonal migration of the Kuroshio were also studied. In summer the counterclockwise circulation and cold dome migrated shoreward/seaward with the intra-seasonal migration of the Kuroshio. In winter the Kuroshio either intruded onto the shelf just off the northern tip of Taiwan or slightly further north. The resulting flow patterns north of Taiwan varied with the path of the intruding Kuroshio. Though the impact of the Taiwan Strait outflow on the flow pattern north of Taiwan was not negligible, it was not as great as the impact of the Kuroshio. Conversely, the intrusion of the Kuroshio strongly influenced the Taiwan Strait outflow. In summer counterclockwise circulation blocked the Taiwan Strait outflow and directly interacted with the Kuroshio. In winter the outflow joined with the on-shelf Kuroshio north of Taiwan.