TOPIC Frontier Newsletter No.15 Jul.2001

Frontier Observational Research System for Global Change
Here, we like to introduce activities of FORSGC, which collaborates with FRSGC for the global change research. Dr. Naoto Iwasaka, a sub-leader, who belongs to Oceanic Variation within Semi-Surface and in the Middle Layer of the Climate Variations Observational Research Program, will explain his research results.

Observation and monitoring of the subsurface and middle layers of the world ocean by using profiling floats

Dr.Naoto Iwasaka (Climate Variations Observational Research Program)

We have been studying physical aspects of subsurface and middle layers of the ocean that are very important in long-term weather forecast and climate change prediction. Our group, in cooperation with the Ocean Observation and Research Department (OORD), Japan Marine Science and Technology Center, have been playing major roles in "The Establishment of Advanced Ocean Observation System", so called Japanese ARGO, under "The Millennium Project" of the Japanese Government. The project is a substantial part of the International ARGO project that will construct a monitoring system of upper and middle layers of the world ocean by using newly developed instruments, i.e. profiling floats.

The goal of our research group in the ARGO project is to develop the monitoring system of upper and middle layers of the western Pacific Ocean, the eastern Indian Ocean and other oceans. The scientific subjects of the group are 1) subduction processes in the North Pacific, 2) variations of the Kuroshio re-circulation, 3) circulation and refreshment of water masses in the middle layer of the subtropical North Pacific, and 4) thermal structure and variations in the upper and middle layers of the North Pacific.

By the end of Fiscal 2000, the group and OORD have deployed 17 profiling floats in the north, middle and south of the Kuroshio Extension during several cruises of R/V Mirai. We developed the technique of ballasting the floats using the high-pressure tank in JAMSTEC and the method of calibrating the CTP sensors. We also performed a series of field tests in the tropical Pacific for comparing several types of CTP sensors. We have established the data processing, quality control and archiving system of the float observations. We also have developed a method for deployment design based on outputs of an ocean general circulation model and a physical oceanographic quality control technique for the float observations based on historical hydrographic data. A case study of water mass distribution and vertical structure of a cyclonic eddy south of the Kuroshio Extension was done by using the float observations.

In Fiscal 2001, we are going to perform again the CTP sensor-comparison test. A field test to investigate biological effects on the CTP sensor will be held in Sekinehama this summer. We will begin to develop techniques to utilize the float data in a data assimilation model. More than 60 floats will be deployed in the Western Pacific and 10 in the eastern Indian Ocean for construction of the observation network. Eventually we will deploy more than 400 floats in the Western Pacific, Indian Ocean and other regions by the end of 2004. This year, we are going to analyze water mass distributions north and south of Kuroshio Extension by using the accumulated float observations.

Member's photograph Group members:
Front row from left, Iwasaka, Shikama, Suga and Ichikawa,
back row from left, Oka, Miyazaki, Matsuura, Jiang, Yang and Kobayashi

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