The ultimate goal of the commencing Triangle program is the thorough investigation of NP-DICE. Within this framework of experiments, a suite of projects have been proposed to address pending key questions concerning the Kuroshio Extension [Mitsudera, 1998]. Principal aims are to investigate the interaction between the meandering Kuroshio Extension and its surrounding waters, the subtropical and subarctic gyres, to understand the decadal/interdecadal modulation of the Kuroshio recirculation, to establish pattern of transfer of water and/or properties across the Kuroshio front and to determaine the role of the Kuroshio Current system in the heat and freshwater budgets of the North Pacific [Mitsudera, 1998].
INTERMEDIATE WATER IN THE KUROSHIO EXTENSION
A wealth of research has been conducted on the Kuroshio Current and its Extension [Kawabe and Taira, 1998; Talley, 1993; Yasuda, 1997], using conventional hydrographic methods as well as surface drifters. Studies on the origin of the NPIW provide two alternate explanations for the formation process of a NWIW low salnity layer at 26.7 - 26.9 σθ: (1) the freshening of waters within the subarctic gyre by vertical diffusion und the subsequent lateral exchange of these low salinity waters into the subtropical gyre along the Kuroshio Extension [Reid, 1965; Talley, 1993], or (2) the formation of a pycnostat of low salinity water in the Okhotsk Sea, which, by mixing with subarctic water, form Oyashio water which will then mix isopycnally with the saltier Kuroshio water. Yasuda recently provided an elaborate scheme on how vertical velocity, salinity and potential vorticity distributions of the Kuroshio and Oyashio currents interact to form the salinity minimum of the NPIW [Yasuda, 1997].
Figure 1: Map of the central ?Triangle program" region. Currently available RAFOS floats trajectories (low-passed filtered) [Riser, 1998] are included in black launch positions are indicated by a dot. Displacement of proprietary WOCE RAFOS floats (Dr. Shikuma) are indicated by straight blue lines.
Yasuda [1997] suggests, that near the sea-suface, the influence from the fast flowing, saline Kuroshio dominates the inflow from the slower, fresh Oyashio Current, producing a saline blend. At intermediate depth however, the speeds of both Currents are similar and a fresher blend develops upon mixing. Below the intermediate layer, salinities within both currents are increasing with respect to the intermediate layer, producing a saline mix as well.
