Special Topic: Kuroshio
The JCOPE Ocean Forecast System
Kuroshio is a ocean current which brings warm sea water from East China sea to south of Japan. Yet due to the flow change by the large eddies of few hundred kilometers near Kuroshio current, it changes the flow pattern, which affects the climate of Japan significantly. Studying the Kuroshio current is one of the research activities of Frontier Research System for Global Change (FRSGC) and Frontier Observational Research System for Global Change (FORSGC). In this edition, we would like to introduce some research activities concerning Kuroshio current carried out by FRSGC and FORSGC.
Frontier Research System for Global Change (FRSGC)
Climate Variations Research Program
Mr.Yasumasa Miyazawa

Realtime Ocean Forecast System

Recent development in the global ocean observation system such as the ARGO*1 enables us to effectively forecast oceanic conditions on a real-time basis. As a part of the JCOPE*2, we have developed a high-resolution ocean forecast system. The routine prediction of oceanic variation which we call "ocean weather forecast", combining with in-situ verifications, will significantly contribute to improve atmosphere-ocean models for prediction of longer-term climate change and also to be applied for fishing, recreation, and Ocean Safety, etc.

High-resolution Ocean General Circulation Model
The present ocean model is based on one of world community models, which is called Princeton Ocean Model (POM). A high-resolution, regional model with spatial grid of 1/12 degree and 35 sigma levels is embedded in a low-resolution basin-wide model with spatial grid of about 1/4 degree and 21 sigma levels (Fig.1). The former model domain covers the northwestern Pacific ocean (117E-180E, 12N-56N) and its lateral boundary condition is specified using the one-way nesting method from the latter model. The model is driven by wind stresses, and heat and salt fluxes. The wind stress and heat flux field are calculated from the 6-hourly NCEP/NCAR reanalysis data and the QuikSCAT Near-Realtime (NRT) data product using the bulk formula. The salinity at the surface is restored to the monthly mean climatology with a time scale of 30 days. Synoptic variations in the northwestern Pacific ocean are well simulated using the high-resolution model.

Fig. 1 Topography of the JCOPE model

Data assimilation
Using an optimum interpolation (OI) method, weekly mean various data are created from sea surface height anomaly (Jason-1 and Geosat Follow On), sea surface temperature (NOAA/ AVHRR), and subsurface temperature/ salinity profiles including the ARGO data (GTSPP). To consistently assimilate those data into the model, the multivariate optimum interpolation method is adopted to estimate the analysis data of temperature/salinity in vertical column. The analysis data are smoothly introduced into the model using the Incremental Analysis Update(IAU). Two months forecast run driven by the monthly mean climatological surface forcing is weekly updated. The data assimilation creates the initial state with root mean square (RMS) error of about 1 degree Celsius for temperature and 0.2 psu for salinity. Magnitude of the RMS error, which depends on simulation skill, assimilation method and quality of data, is consistent with the OI error.

Current Status

The system has shown a forecasting skill of about one month during the real-time experiment in 2003. In particular, the system has successfully predicted a small meander propagating eastward along the Kuroshio south of Japan during March-May 2003 (Fig. 2). However, the system failed to predict decay of the meander in June 2003. Increasing vertical levels of the model, we are trying to improve the forecasting skill of this event.

Fig. 2 Snapshots of sea surface temperature from 26 April to 9 May 2003.
Upper: Observation from the NOAA satellites provided by the Japan Coastal Guard.
Lower: Forecast of the JCOPE system from 16 APR. 2003
*1 Argo is a project that is conducted under the World Meteorological Organization (WMO), the Intergovernmental Oceanographic Commission of UNESCO (IOC) and other related institutions. The aim of the project is to build a real time, high resolution monitoring system for upper and middle layers of the world ocean.
*2 Japan Coastal Ocean Predictability Experiment
   C l o u m n
Provision of Japan Coastal Ocean Predictability Experiment (JCOPE) Data
The JCOPE group of Climate Variations Research Program, Frontier Research System for Global Change, has been conducting "Ocean Weather Forecast", by using the weekly (every Saturday) updated ocean conditions assimilating the observational data as a initial stage. Its prediction result has been open to public through our website. (http://www.jamstec.go.jp/frsgc/eng/jcope/index.html). We have decided to provide the output data (two days mean grid data of sea surface temperature, salinity, and sea surface height of after 14th November, 2002) to those who are interested.

The JCOPE group will work for further accuracy of data, by referring the users' comments. Meanwhile, we will provide the outputs of two months prediction, which has been conducted as a trial. We are hoping that its relevancy and effectiveness will be discussed through people in utilizing this data.

For details, please contact JCOPE group: jcope@jamstec.go.jp
Frontier Newsletter/No.24
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