While the floals will provide a handle to the current's position and a direct description of its meanders, the moored CTD/current meter array can be used to verify where, with respect to the thermohaline structure of the current, the float is positioned. In turn, the float velocity information can be used to derive a level of reference for geostrophic calculations from the moored and ship-borne CTD data. Curvature vorticity derived from the floats trajectories, could be combined with stretching vorticity from the CTD's and planetary vorticity to provide absolute vorticity information. This could then be used to characterize the location of the vorticity front which supposedly hampers the cross-frontal and intergyre exchange.
The combination of float trajectories with inverted echosounder data (IES) has been most fruitful inseveral Gulf Stream experiments [Kelly and Watts, 1994]. While the IES provides the depth of the main thermocline, which may be used to trace the location of the main front, the float trajectories provide the flow field at greater depths and, combined, a handle to the vertical structure of the current. Additional benefits will stem from a joint analysis of float data and sea-surface temperature (AVHRR) images, which can be used to link individual trajectories to surface patterns and dynamic processes and to explore the vertical extend of sea-surface features. The tomographic array will provide a vertically resolved temperature structure, which could be exploited for the Lagrangian study to precisely determine the speed of sound across the study area and hence to obtain an improved precision of the float trajectories.
With the repeated deployment of RAFOS floats into the core of the Kuroshio at its transition to the Kuroshio Extension, it is hoped to achieve the following tasks:
1.) To determine the mean position of the Kuroshio Extension at intermediate depth
2.) To determine the magnitude and frequency of deviations of the Kuroshio Extension from its mean position
3.) To determine the mean and variability of the speed of the Kuroshio Extension
4.) To observe and determine the cross frontal exchange between the Kuroshio Extension and the surrounding waters
5.) To observe the interaction between topographic features and the flow at intermediate depth.
6.) To observe the flow patterns associated whit the Kuroshio Extension, in particular the existence of a downstream bifurcation
7.) To provide direct measured velocities in connection with the suggested array of inverted echo sounder, tomographic and CTD/current meter mooring array.
ACKNOWLEGEMENTS
The enthusiasm and dedicated support by T. Yamagata for the proposed project significantly encouraged the author to explore this line of work and to draft a first proposal. The manuscript also benefited from extended discussion with H. Mitsudera and N. Hogg during the Kyoto Triangle Symposium. T. Rossby is gratefully acknowledged for his support during the preparatory phase of the associated oral presentation and for the provision of his Gulf stream data and animation program. Financial and logistic support by the Frontier Research System for Global Change (FRSGC) enabled the author attend the Kyoto Triangle meeting and to give presentations at FRSCG and JAMSTEC.
