Numaguti, A., M. Kimoto, T. Nakajima and M. Takahashi,
1995: Validating clouds and the hydrological cycle in the CCSR/NIES AGCM.
Abstracts of the First International AMIP Scientific Conference, Monterey,
California, 46.
The performance of the CCSR/NIES AGCM, which was recently developed
by the Center for Climate System Research, University of Tokyo and the
National Institute for Environmental Studies is examined mainly from the
aspect of clouds and the hydrological cycle. This model is newly developed
and has not participated in the AMIP program. The model uses the spectral
transformation method in the horizontal and grid differentiation on sigma
coordinates in the vertical. The physical parameterization includes a sophisticated
radiation scheme using the 2-stream k-distribution method, a simplified
Arakawa-Schubert cumulus scheme, a prognostic cloud water scheme, and turbulence
closure scheme with cloud effect.
Results of 10-year integrations with T21 and T42 versions of the model
are compared with ERBE and ISCCP products. Both versions have 20 vertical
levels. Zonal mean values of cloud radiative forcing as well as OLR and
planetary albedo compare well with satellite-derived values. However, there
are several conspicuous discrepancies in longitudinal distribution. Their
revision through adjustment of parameterization schemes is the subject
of this presentation. The discrepancies include low OLR and high albedo
within the subtropical anticyclonic regions over the ocean. The low-level
cloud is too dense in these regions. On the other hand, the low-level cloud
amount over the land is found to be too small. One of other defects of
the model simulation is a severe dry bias of the tropical lower troposphere.
Some of these aspects could be alleviated by adjusting treatments of clouds
and sub-grid scale turbulence.