Kuroshio variations in the upstream region as seen by HF radar and satellite altimetry data

Variations of the position and speed of the Kuroshio are studied by a combination of high-resolution high-frequency (HF) ocean radar data and wide-coverage altimetry data. The speed of the Kuroshio and its position are determined along 123.35° E northeast of Taiwan from daily maps of surface geostrophic velocity estimated from HF radar data from August 2001 to February 2005. These two are found to be well correlated for mesoscale variations with periods of a few months, as the Kuroshio tends to be faster (or slower) when its axis moves south (or north). This tendency is significant in summer when the Kuroshio is seasonally intensified and well-defined in the HF radar data. By taking correlation with the sea surface dynamic height anomaly observed by satellite altimeters, these Kuroshio variations in the East China Sea are found to be induced by merging of mesoscale eddies from the east at 21° N and by coincident Kuroshio meanders east of Taiwan.