The CSK (Collaborative Study of Kuroshio and adjacent region) was the first project of the Intergovernmental Oceanographic Commission (IOC) with the aim to enrich the knowledge of oceanography and fisheries in the Kuroshio region. The CSK includes participants and supporter from 12 countries. Its area extends from the longitude from 160°E to the mainland of Asia and latitude from 4°S to 47°N, including the East China Sea, Southern Sea of Japan and the Eastern Philippines Sea. Kuroshio data center had received 16,727 stations data from 435 cruises between 1965 and 1979, and 6 volumes of “CSK Atlases” were compiled after the completion of the project. Since the completion of the CSK, many multi-national, bilateral, and national projects and studies have been conducted aiming to understand more about ocean circulation and variations in the Kuroshio and its adjacent regions as well. These projects are listed as follows:
For the Kuroshio in the East China Sea, the Japan Meteorological Agency (JMA) has conducted quarterly observations since 1987, including a conductivity-temperature-depth profiler (CTD) and a shipboard acoustic Doppler current profiler (ADCP) at the PN and TK sections, which cut across the Kuroshio in the East China Sea. The Kuroshio edge exchange processes (KEEP) was a multidisciplinary study on the internal cycling of material, especially carbon, within the East China Sea Shelf. The project has been ongoing since 1989, and its primary purpose was to investigate the processes for material exchange between the East China Sea Shelf and the adjoining Kuroshio. WOCE PCM-1 array was a joint US – Chinese Taiwan collaborative effort, which consisted of 11 subsurface moorings distributed along the Ilan Ridge between the east coast of Taiwan and the southern Ryukyu Island of Iriomoteto from 1994 to 1996. The array was used to study the volume and heat transport of the Kuroshio.
There are several projects related with the origin area of the Kuroshio. The Origins of Kuroshio and Mindanao Current (OKMC) which was sponsored by Office of Naval Research, United States from 2011 to 2014. The participating institutions include Scripps Institution of Oceanography, Woods Hole Oceanographic Institution, and Applied Physics Laboratory/University of Washington. Gliders, drifters, and floats are used by the project to study the transport and flow patterns, temperature/salinity properties, and eddies and their effect on mean flow in the CKS and its adjacent regions. Observations of the Kuroshio Transport Variability (OKTV) was sponsored by Chinese Taiwan from 2012 to 2015. This project first analysis the time series of the full-water column absolute transports and velocities generated from the PIESs’ observations east of Taiwan, the result of which were compared with the analogous time series derived from PIESs deployed across the Kuroshio northeast of Luzon. The Northwestern Pacific Ocean Circulation and Climate Experiment (NPOCE) is a multi-national, multi-institutional, and multi-platform program, led by the institute of Oceanology, Chinese Academy of Sciences (IOCAS). It is endorsed by Climate Variability and Predictability (CLIVAR) as an international cooperative program. As an important part of the field experiment of the NPOCE, two subsurface moorings were deployed along 18.0ºN section (122.63ºE and 122.93ºE) between November 2010 and October 2012, in order to maintain the long-term direct observations of the Kuroshio at its origin. Later, three subsurface moorings were deployed along 18.0ºN section (122.7ºE, 123.0ºE, and 123.3ºE) in January 2017 and have continuously measured three dimensional velocity until now. Most importantly, one of three moorings (123.0ºE, 18ºN) had realized real-time transmission of velocities in the upper 1000 m depth.
Until recently, there have been quite limited high-resolution observations in the Kuroshio extension region. Kuroshio Extension System Study (KESS) was a collaborative effort by the Woods Hole Oceanographic Institution, the University of Rhode Island, and the University of Hawaii. The goal of 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. This project launched from 2004 to 2006 and funded by US National Science Foundation (NSF), which deployed an observing array consisting of Argo profiling floats, moored-profiler, moorings, Current-Pressure equipped Inverted Echo Sounder (CPIES) as well as a surface buoy (KEO) located south of the Kuroshio. North of the Kuroshio, another buoy (JKEO) was deployed by the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) Institute in 2007. However, JKEO has been discontinued after the end of the Japanese HOTSPOT project in 2015. Following KESS and Japanese HOTSPOT projects, a new observational project in the Kuroshio extension region under IOC Sub-Commission for the Western Pacific (WESTPAC), Air-Sea Interaction in the Kuroshio Extension and its Climate Impact (AIKEC) led by the Ocean University of China (OUC) and the Texas A&M University (TAMU), was setup to maintain continuous and sustainable observations in this region. This project focuses on the multi-scale variability in the Kuroshio Extension Region, such as eddy-Kuroshio interaction and eddy induced air-sea interaction. In the first cruise in late March 2014, 17 Argo-profiling floats with enhanced daily sampling in an anticyclonic eddy (AC) south of the Kuroshio Extension (KE) was deployed, along with one subsurface mooring and two gliders near KEO buoy. After 2014, there are 6 cruises conducted. Now two subsurface moorings (M1 and M2) are fixed for long-term observation, M1 near KEO and M2 located in the north of the Kuroshio Extension (150.0ºE, 39ºN). A test buoy made by TAMU and OUC was also deployed near M2 from October 2017 to May 2018.
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