Horizontal water exchange across KE
Behavior of two groups of drifters, separalted artificially by their deployment north or south of 35°N (Figs.1a and b, respectively) revealed the lack of drifters having visited both Subtropical and Subarctic Gyres. Mixing zone,defined by the southern edge of area covered with “northern” drifters and the northern limit of the “southern” ones is located in the northern part of KE and remains as narrow as 2-3°N at 140-180°E that contradicts to traditional ideas of large-scale mixing. Indeed, drifters ensemble, composed of buoys, having penetrated into the mixing zone (Fig. 1c) does behave typically for turbulent jet. One may estimate diffusion and fluxes with statistical methods and miss their actual vanishing contribution into the inter-gyre exchange. At the same time, mixing seems to be significant north and south of KE. This effect can be due to isopycnals outcropping at the fronts replacing horizontal motions by isopycnal ones.
Mean velocities, their variability and optimization
Fig. 2 displays mean velocities and their variability averaged within 1°N×1°E boxes, for which data are available. When Fig. 2b agrees well with eddy kinetic energy distribution, obtained in previous studies [3], mean velocity field reveals, along with Kuroshio Current, KE, Tsushima Warm Current, Kamchatka Current and Subtropical Countercurrent (STCC), the lack of distinct Oyashio Current and the existence of strong and narrow eastward jet associated with SF.
