Present-Day Climate and Climate Sensitivity in the Meteorological Research Institute Coupled GCM Version 2.3 (MRI-CGCM2.3)

Abstract

A new version of the Meteorological Research Institute (MRI) coupled general circulation model MRI-CGCM2 (MRI2.3) is developed and compared with the previous version (MRI2.0). The cloud scheme includes diagnostic function for cloud amount separately specified for convective and layer clouds, which is one of the major modifications contributing to the improved model performance. MRI2.3 exhibits better agreement with the observations in many aspects of present-day climate simulations, including the global energy budget, meridional distributions of shortwave and longwave radiation at the top of the atmosphere, and geographical distributions of surface air temperature and precipitation. The effective climate sensitivity of each version is evaluated based on an experiment with a transient (1%/year) increase of carbon dioxide concentration. The effective climate sensitivity of MRI2.3 (2.9 K) is about twice that of MRI2.0 (1.4 K). The change in the cloud-forcing response, particularly for shortwave cloud forcing, is essential for increasing climate sensitivity. A difference in tropical low-level clouds over the subsidence regions contributes significantly to the difference in cloud-forcing changes in response to a climate change. Analyses based on circulation regimes, defined by the vertical velocity at the mid-troposphere, suggest that the cloud-forcing response in the tropics is controlled more by thermodynamic characteristics, such as changes of the stability in the lower troposphere, rather than by large-scale circulation changes, such as a change in the subsidence strength.

A New Global Climate Model of the Meteorological Research Institute: MRI-CGCM3 —Model Description and Basic Performance—

“…Consequently, the climate sensitivity of MRI-CGCM3 is 2.11 K (¼ 4.22/2) for doubling of CO 2 concentration. This value is marginally in the lower range of multi-model results (2.1 K to 4.4 K) estimated from slab mixed layer ocean equilibrium in IPCC-AR4 and is only 73% of the climate sensitivity 2.9 K (equilibrium response with slab ocean) of MRI-CGCM2.3.2 (Yukimoto et al 2006). It is di‰cult to estimate real climate sensitivity from the observations, due to complicated variations induced by various forcings and internal climate variability.…”

“…The Meteorological Research Institute (MRI), with the former climate model MRI-CGCM2.3.2 (Yukimoto et al 2006), contributed to the IPCC-AR4 by providing results from numerous experiments for the third phase of the Coupled Model Intercomparison Project (CMIP3). For the experiments, MRI-CGCM2.3.2 used global flux adjustments (Manabe and Stou¤er 1988) for heat and freshwater, and partially for momentum.…”

Seasonally asymmetric transition of the Asian monsoon in response to ice age boundary conditions

“…Readers are referred to Shibata et al (1999) for details. The AGCM is used for the global ocean-atmosphere coupled GCM developed at the Meteorological Research Institute (MRI; Yukimoto et al 2006) for climate variability and change research. Here we employ a version with triangle truncation at zonal wave number 42 (T42) and 30 vertical layers on hybrid sigma-pressure coordinates.…”

A Role of Zonal Gradient of SST between the Indian Ocean and the Western Pacific in Localized Convection around the Philippines

“…The model we use is AGCM in MRI-CGCM2.3, an airsea coupled model (CGCM) developed by Meteorological Research Institute in Japan (Yukimoto et al 2006). The AGCM is a global spectral model, which we ran at T42 resolution and with 30 sigma-pressure coordinate levels in the vertical with model top at 0.4-hPa.…”