A regional climate change projection over East Asia

The regional scale climate change over East Asia is evaluated using a regional climate model. The model is based on the Regional Atmospheric Modeling System developed at Colorado State University and modified at National Institute for Environmental Studies. The modification was focused on the physical processes including radiation, cumulus convection and land surface hydrology because those processes become especially important in a long-term integration of the model. The model domain includes Japan islands, Korean peninsula and the eastern part of China. The horizontal grid resolution is set to 50km.

To evaluate the performance, the model was driven by twice-daily ECMWF analysis data of 2.5 degree horizontal resolution. Two year-long integrations for 1993 and 1994 are made and validated against various observational data. The model simulated the spatial pattern of precipitation and outgoing longwave radiation over East Asia and the annual temporal variations of precipitation and surface air temperature over various regions of Japan fairly well. It is suggested that the simulation of Baiu, the persistent precipitation band over Japan islands mainly in June, is strongly sensitive to cumulus parameterization. An Arakawa-Schubert type cumulus scheme tends to fail the simulation of Baiu, while the simulation is improved when the scheme is modified to consider the suppression of cumulus convection under a dry environment. The inter-annual variability of the climate over East Asia between 1993 and 1994, especially the contrasting cool summer in 1993 and hot summer in 1994 over Japan, is represented well by the model.

For projecting the future climate change, the model was driven by the twice-daily outputs of two GCM experiments with T63 horizontal resolution. The atmospheric concentrations of greenhouse gases and sulfate aerosol and the distribution of sea surface temperature is differently prescribed for the two experiments. One is for the present climate and the other is for the climate when the atmospheric concentration of greenhouse gases is doubled. The GCM used is CCSR/NIES AGCM, whose physical parameterizations are fully consistent with our regional climate model. The sea surface temperature of the doubled-greenhouse gases climate is taken from the transient experiment with CCSR/NIES coupled ocean-atmosphere GCM. Based on the comparison between the two regional model experiments, the characteristics and mechanisms of the regional climate change over East Asia will be presented.