Marine Ecosystems Research Department - jamstec japan agency ...

JAMSTEC 2002 Annual Report
Frontier Research System for Global Change
atmosphere, which may be coupled with climate
change near the surface. Hence, numerical studies
should be conducted with an improved version of the
climate model.
Behaviors of internal gravity waves and those influences
on the general circulation should be investigated
by performing numerical experiments with an ultrahigh
resolution GCM, since they play very important
roles in the middle atmosphere.
This year, the vertical domain of the atmosphere
GCM was extended to the mesopause level (~ km).
The importance of various atmospheric waves controlling
mean states and variability of the middle atmosphere
was confirmed by a series of numerical experiments.
For this purpose, hundreds of sets of horizontal-and-vertical
resolution and physical parameters of
the model were tested. Simultaneously, numerical
resources of the Earth Simulator required for these
simulations were checked. The highest resolution simulation
performed to date is T L, i.e., .
degrees in both longitude and latitude and m in
vertical.
The sigma vertical coordinate system used in the
original GCM was replaced with a sigma-pressure
hybrid coordinate. As a result, the accuracy of transport
processes in the stratosphere was improved. On
the other hand, causal mechanisms of cold and moist
biases near the tropopause were investigated, though
they are yet to be solved.
Subject 7: Research Development of the Advanced
Four-Dimensional Data Assimilation System Using a
Coupled Atmosphere-Ocean-Land Surface Model
Toward the Construction of High-Quality Reanalysis
Datasets for Climate Prediction
The main objective of this research approved by the
MEXT(Ministry of Education, Culture, Sports, Science,
and Technology) as part of the "RR" Project is to
construct an innovative four-dimensional data assimilation
system capable of providing a high-quality comprehensive
dataset referred to as "reanalysis dataset".
This is stimulated by recent remarkable progress in the
earth observing system and numerical models. Though
observations are still sparse in time and space, their
synthesis with the state-of-the-art general circulation
models (GCMs) has the ability to produce a -dimensional
(D) reanalysis dataset. Such datasets are vital
for more accurate seasonal to interannual (S-I) prediction
and for a better description of the dynamical state
of the global warming and hydrological cycle.
Data assimilation (DA) studies so far have shown
that variational (VAR) assimilation approaches using
GCMs are the most likely means of creating dynamically
consistent datasets. However, the computational burden
required is quite heavy (at least times that of
simulation models). This limited us to use the D-VAR
model when applying the VAR method to the climate
system covering the entire globe. The D-VAR method
has the potential to ensure good dynamical consistency
in space, but it is not the case for the model time trajectory.
The Earth Simulator (ES) could give a breakthrough
for such limitation. That is, huge computational
capability of ES enables us to construct an advanced
D-VAR coupled DA system (using atmospheric and
ocean GCMs) for the first time. This could greatly contribute
to better understanding dynamical and thermodynamical
processes in the climate system on the earth
and to increasing skills on climate prediction.
In order to realize our purpose, five functional components
are organized in this program as shown in
Figure :
Theme : Development of data assembly systems, quality
control, and international data network.
Theme : Development of a high-resolution climate
GCM on ES.
Theme : Development of D-VAR coupled DA system
on ES and construction of a reanalysis
dataset in s and its validation.
Theme : Improvement of initialization and predictability
by a nonhydrostatic coupled GCM.
Theme : Development of distributed sheared-database
system with DODS/LAS/CAS/EPIC.
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