| Special Topic: Kuroshio |
| The JCOPE Ocean Forecast System |
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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. |
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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.
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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.
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| 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
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| *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 |
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| 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
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