Development of the Japan/East Sea forecasting system
Naoki Hirose, Sergey M. Valramov, Jong-Hwan Yoon, Tetsuo Yanagi
Dynamics Simulation Research Center, Research Institute for Applied Mechanics, Kyushu University
6-1 Kasuga-kouen, Kasuga 816-8580, Japan
Corresponding e-mail address: hirose@riam.kyushu-u.ac.jp
Abstract: We have been developing an integrated system to predict environmental variables in the
Japan/East Sea. The nowcast and forecast of the water properties are expected to contribute to the ocean
science and societal applications such as fish resource and pollutant control or and marine weather forecast
in the region.
Recent developments in the Japan/East
Sea (JES) modeling made an operation of the
forecasting system possible starting from October
2004. The system produces short-term forecasts
up to 5-6 days and provides nowcast and longterm forecast of basic oceanographic variables for
the JES. The forecasted variables are the water
temperature, sea level anomalies, currents,
salinity, and so on. The results are opened for
wide range of users through a web site at
http://jes.riam. kyushu-u.ac.jp/ .
surface is explicitly calculated by a barotropicbaroclinic splitting technique and enables the tidal
simulation. The model is further implemented by
generalized Arakawa scheme (Ishizaki and Motoi,
JAOT, 1999), a turbulent mixing model (Noh and
Kim, JGR, 1999), an isopycnal diffusion scheme
(Gent and McWilliams, JPO, 1990). The
operational version has 1/12° grid spacing and
thin top layer of 5 m thickness. The model well
reproduces many oceanographic processes in the
JES such as the Tsushima and the East Korean
Warm Currents (TWC, EKWC) and their
variabilities, deep water formations, or tidal
variations.
2.
4.
1.
Introduction
System overview
The system flowchart is shown in Fig. 1.
The central part of the system is an original 3D
OGCM named RIAM Ocean Model (Lee et al.,
OPR, 2003), which is accompanied with an oil
spill drift and fate model (Varlamov, JMST, 1999)
and with an ecosystem model of the JES (Yanagi
et al., 2001). The oil spill drift prediction model
provides the tools for emergency forecasts of drift
and fate of floating and dispersed hazardous
materials in the sea. The ecosystem model will
supply lower trophic level parameters such as
dissolved inorganic nitrogen or phosphorus,
phytoplankton, zooplankton, or detritus.
Fig. 1 Flowchart of the Japan/East Sea forecasting
system.
3.
Model
The RIAMOM solves the primitive equations
assuming the hydrostatic relation at regular
latitude-longitude grid in z-coordinates. The free
Data Assimilation
The long-term assimilation model is driven
by daily-mean surface fluxes estimated by bulk
formulas from the JMA high resolution (~0.1
degree) regional meteorological data. The
sequential corrections have been preformed by
assimilating the satellite altimeter data on a
coarser 1/3° grid for the barotropic and first
baroclinic modes, which is known as an
approximate Kalman filter (Fukumori et al., JGR,
1999). The surface relaxation is simultaneously
made by the high-resolution merged satellite SST
data of Tohoku University with one-day time
scale. Manda et al. (2005) demonstrated that the
restoring the surface temperature to the satellite
observation matches the nonlinear ensemble
Kalman filtering. The inflow open boundary
conditions (Tsushima/Korea Straits) for the
volume transport are now given by long-term
monthly mean data measured by ship-mounted
ADCP, and temperature and salinity are taken
from the results of 1/6° Pacific Ocean model.
Figure 2 shows the sea surface
temperature and currents at October 1, 2004
estimated by the assimilation system for the
southwestern part of the JES. The TWC is
relatively stable at the southwestern entrance and
separated into two branches by the Tsushima
Islands. The two flows generate leeward eddies
by interacting each other. The western boundary
current of the EKWC and travels north up to 37°N
along the coast and contributes meandering of the
Polar Front at this time. The warm water
transported into the JES tends to be unstable and
to form mesoscale eddies, which are easily found
by the streamlines on the map. The positions and
strength of the eddies are crucial information for
fisheries. The present estimates indicate smallscale eddy structures and the cold water along the
North Korean coast.
degradated etc. Particles tracking method is
adopted, that includes effects of oil transport
by wind and sea currents, buoyancy, three
dimensional random diffusion and oil coastal line interaction. Parameterizations for
the oil evaporation and emulsification at the
sea surface and for the biochemical
degradation in the water column are adapted.
As result the oil emulsion viscosity and
density are changed. The last value as well
as particle size influences the oil buoyancy
and so the penetration of oil into the water
depth (dispersion formation). Random walk
technique is used for simulation of vertical
and horizontal turbulent mixing. Mixing length
scales depended from the surface wind and
current, counting for larger rate in the stormy
weather. In calm weather oil particles could
resurface by the buoyancy effect.
7.
Fig. 2 Estimated surface temperature and currents in
the southwestern part of the JES at 10/1, 2004. The
temperature variation is shown by colors ranging from
18 to 25°C.
The assimilation of the inflow condition at
the Tsushima/Korea Straits is underway. The
long-term forecast will be performed by switching
the forcing with climatology.
5.
Short-term forecasting
The short-term simulation and forecast
version of model includes the tidal prediction
module driven by the tidal body forcings and sea
level anomalies at the open boundaries. The
surface fluxes are estimated with the TOGACOARE bulk parameterization accompanied with
estimation of radiative fluxes with daily variations.
It also adopts the relaxation to the Tohoku
University SST data at the analysis stage as is
done
in
the
assimilation
model.
The
meteorological data are currently supplied by the
NOGAPS analysis and forecasts up to 144 h (6
day). Sine one day is consumed by downloading
remote data and model computation, the
prediction is made for up to 5 days.
6.
Oil spill simulation
The oil spill model starts its forecasting
in any emergency cases. It presents the
spilled oil as an ensemble of particles. Each
particle is characterized by its position on the
plane and in the depth, diameter, and
physical properties – initial density, viscosity,
fraction of water in oil, fraction evaporated,
Servers
The system is designed to be automatic
for operation in real time. The local data
server stores the static data of topography
and climatological data, and calls remote
sources for the meteorological data or
satellite data by regular ftp. In present
configuration, the short-term and long-term
JES simulation and nowcast are produced by
the RIAMOM every 12h and one month,
respectively. The results are available to the
public
through
the
WWW
server
(http://jes.riam.kyushu-u.ac.jp/). It provides an
interactive interface for flexible visualization.
It requires approximately 2.5 hours for model
run predicting for 6 days on 2 Itanium CPUs
workstation with OMP parallelization.