Marine Ecosystems Research Department - jamstec japan agency ...

Japan Marine Science and Technology Center
Frontier Research System for Global Change
subtropical jet stream are properly maintained. Only
under this large-scale condition, the realistic Baiu
frontal precipitation zone is formed in the model.
The simulation for January indicates the reasonable
quasi-periodic development of extratropical cyclones
over the east coast of the Asian continent and associated
polar air outbreak. A typical polar low is formed
over the coastal sea area ~km west of the major
extratropical cyclone that developed over the
Northwestern Pacific Ocean, under the influence of a
short wave trough. The strong heating due to the energy
supply from the sea surface contributes to the genesis
of the polar low through decreasing the vertical stability
and sustaining the thermal gradient.
Takeshi Enomoto primarily investigated the summer
climate in east Asia using observed data and model
output. He extended his research on the Ogasawara
(Bonin) anticyclone that appears in late summer over
Japan to study its interannual variability. He confirmed
a robust relation between the undulation of the subtropical
jet and intensification of the high in its inter annual
variability using NCEP Reanalysis, which is consistent
with his previous numerical work.
In association with researchers in other program at
FRSGC and the Earth Simulator Center, he also performed
a -km mesh global simulation of the
Baiu/Meiyu frontal zone using AFES (AGCM code for
the Earth Simulator) of the CCSR/NIES model.
b. Next-generation Model Development
b-. Next generation Atmospheric Modeling
A new high resolution atmospheric general circulation
model referred to as NICAM (Nonhydrostatic
ICosahedral Atmospheric Model) is being developed.
It is a grid model with an icosahedral structure and is
based on the non-hydrostatic equations. The main target
is high-resolution climate simulations by improving
representation of cumulus convection with higher resolutions.
This project started in and to date a
dynamical core of the global model has been developed.
We are running the new model on the Earth
Simulator and found that the computational efficiency
of NICAM is superior to that of a well-tuned spectral
transformation model at high resolutions with a grid
size smaller than km.
As a subset of NICAM, we are also developing a
regional Cartesian non-hydrostatic model. The model
structure is almost parallel to the global icosahedral
model, so that new dynamical and physical schemes
are tested in order to be installed to the global model.
Both models are based on the newly considered flux
form Eulerian scheme, which guarantees conservation
of mass and total energy. We are introducing physical
processes to the regional model and tesing their performances.
We are also performing radiative-convective
equilibrium experiments to study interaction
between clouds and radiation.
We have performed the standard experiments proposed
by Held and Suarez () and compared the
results with those obtained with the CCSR/NIES spectral
model adapted to the Earth Simulator, called AFES
(Shingu et al., ). Both models are run as the
dynamical cores, i.e. no physics are included. We
found that the result of NICAM is almost comparable
to that of AFES at the resolution glevel (∆x km)
for NICAM and T for AFES.
Figure compares the computational time
required for one time step integration using the Earth
Simulator. We use nodes where each node has
processors and the corresponding peak performance is
T Flops. The abscissa is the maximum total wave
number N of the triangular truncation in spectral model
or the minimum horizontal wavelnegth λ min corresponding
to N. Figure shows that while the curve for
AFES approaches asymptotically to the line N , the
curve for NICAM approaches the line N as resolution
becomes higher. If we interpret the resolution of
NICAM as λ min = ∆x, this shows that NICAM is
almost one-order magnitude efficient in comparison to
AFES for all the resolutions. Even if the resolution of
NICAM is interpreted as λ min = ∆x, the efficiency of
NICAM becomes superior to AFES at higher resolu-
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