Marine Ecosystems Research Department - jamstec japan agency ...

JAMSTEC 2002 Annual Report
Frontier Research System for Global Change
10000
1000
100
10
160
(250km)
320
(125km)
640
(63km)
1280
(31km)
2560
(15.6km)
Truncation wavenumber N (Resolvable scale λ res)
tions than T.
Elapse time for 1 time step [msec] on ES (80 nodes)
3
N slope
gl-7
2
N slope
gl-8
The next case is the result from the life cycle experiment
of extratropical cyclones, which is proposed by
Polvani and Scott () as a standard experiment of
the dynamical core. It compares deterministic stage of
the nonlinear evolution of extratropical cyclones for
about days. We have succeeded in the simulation at
the resolution of glevel (∆x .km) using
nodes of the Earth Simulator.
b-. Next Generation Ocean Modeling Group
5120
(7.8km)
We are developing an ocean circulation model
which has a very high physical and computational performance.
As the first step of this development, an
ocean circulation model, in which we focused on
increasing the computational performance on the
Earth Simulator, has been developed. The model is
based on the Bryan-Cox ocean model and is well vectorized
and parallelized. By improving the data
exchange method, the computational performance of
this model reaches . T flops using nodes on
the Earth Simulator.
In order to realize higher computational performance,
we have started to develop an ocean circulation
model using cubic grid. The cubic grid is generated
gl-9
gl-10
NICAM(λ res=2∆x)
NICAM(λ res=4∆x)
AFES(λ res=2πa/ N)
gl-11
Fig.20 Comparison of computational time for one time step
between NICAM and AFES. The sustained performances
are also shown.
by mapping grids on the surface of a cube to the sphere.
Various mapping methods have already been proposed.
First we tried "conformal" cubic grid and developed an
accurate finite difference scheme including the vertices
and succeeded a long time integration of a shallow
water model by use of this grid. However, this grid system
has a shortcoming; sizes of square shape grids are
larger near the center of the surface of the original cube
and smaller near the original vertices and the ratio
between the largest and the smallest grid size increases
with increase of resolution to reach about at the targeted
resolution, km. Thus this conformal version of
cubic grid tends to loose the "quasi-uniform" nature.
Therefore we decided to abandon the development by
the end of FY . After examination of various methods,
we have come to adopt the method proposed by
Purser and Rancic (). Generally, the cubic grid is
considered to be more advantageous than other quasihomogeneous
grids. The grid is quadrilateral so that it
is relatively easier to introduce the schemes used in
the current ocean circulation models. Moreover,
the cubic grid is structured grid so that the vectorization
and parallelization will be easier and this is crucial to
use the computational power of the Earth Simulator
efficiently. On the way of the development, we derive
Arakawa-Jacobian applied to the entire cubic grid
including the singularities. With the Arakawa-Jacobian,
we developed a momentum-advection scheme which
conserves energy and enstrophy in non-divergent case.
These conservative properties prevent a type of nonlinear
instability caused by anomalous energy cascade so
that we anticipate to simulate well the behavior of
meso-scale eddies which has only a few grids scale
even in the high resolution computation.
We applied the scheme to the standard shallow
water test suite (Williamson et al ). We also
applied the scheme which does not conserves energy
nor enstrophy for comparison. In the test shown below,
no numerical viscosity was applied to clarify the effect
of conservative nature. Fig. shows the free-surfaceheight
field of the simulation of Rossby-Haurwitz
138