The overall goal of the Kuroshio Extension System Study (KESS) is to identify and quantify the dynamic and thermodynamic processes governing the variability of and the interaction between the Kuroshio Extension and the recirculation gyre. Investigators from three US institutions will deploy a state-of-the-art array consisting of moored-profiler and current-meter moorings and inverted echo sounders equipped with near-bottom pressure and current sensors. Profiling floats will monitor the temperature and salinity structure in the recirculation gyre south of the Kuroshio Extension. The KESS array is designed to use these tools synergistically to observe the Kuroshio Extension in a more complete way than any one of them could do alone. In particular, the Inverted Echo Sounders will map features of the jet as they evolve and, in combination with the Moored Profilers, will quantify the cross-frontal fluxes, while the profiling floats will monitor the upper ocean structure around the Kuroshio Extension and its recirculation gyres. KESS will use these combined observations to identify and quantify the dynamic and thermodynamic processes governing the variability of, and the interaction between, the Kuroshio Extension and the recirculation gyre. The proposed approach makes extensive use of satellite data (surface temperature and sea-surface height). The investigators will also collaborate closely with Japanese scientists studying the overall Kuroshio system. The measurements from the KESS array will guide future planning for a long term observational program as part of CLIVAR.