Variability of the Kuroshio Current and its Axis

The variability of current vectors well agree with the horizontal movement of the Kuroshio which is related to the exsistance of small meanders south of Shikoku. The origin of these meanders are propagation from the upstream Kuroshio or directly from the east to the ASUKA-line. It is supposed that the meso-scale eddies from the east produce these meanders.

Time series of daily sampled current vectors measured by Current Meters (CM) at a nominal depth of 700 m, i.e., the upper most mooring depth. Panels are arranged from top to bottom by increasing distance from the coast. The data have been processed by a Godin low-pass filter with a half power gain at 3.9 days. The upward is the direction normal to the ASUKA-line.

Mean velocity during the two years of observation period at the 700 m nominal depth. Data at CM08 (red circle) are available only in the first year.

Latitude-time plot of temperature at the 650 m depth. We estimate the interpolated value at this 650 m depth from the temperature from CM at the 700 m nominal depth, by using vertical profiles of temperature from hydrographic survey (CTD). CM temperature data are low-passed filtered with a Godin filter and averaged over 5 days. Data from CM08 were not available in the second year. It might covers the region between the two red dashed lines. Dots (diamonds) on the top (bottom) show the positions of CM in the first (second) deployment period.

Same as the figure above except for measured absolute current speed at the 700 m nominal depth. The blue line indicates 7 °C isotherm at the 650 m depth. This isotherm and the position of strongest current are highly correlated. We define this isotherm as the axis of the Kuroshio at 650 m.

Same as the previous figure except for geostrophic velocity component at the sea surface normal to ASUKA line calculated from Topex/Poseiden (T/P) altimeter data, referred to the average dynamic sea surface height from CTD and CM data. The white line indicates the location offshore edge of the eastward flow associated with the Kuroshio at the sea surface; it is the location of the highest sea surface height in the Kuroshio region north of 30 °N detected from T/P altimeter data and the temperature at the 650 m from CM shown in the figure above.