20-km-Mesh Global Climate Simulations Using JMA-GSM Model —Mean Climate States—

A global atmospheric general circulation model, with the horizontal grid size of about 20 km, has been developed, making use of the Earth Simulator, the fastest computer available at present for meteorological applications. We examine the model's performance of simulating the present-day climate from small scale through global scale by time integrations of over 10 years, using a climatological sea surface temperature. Global distributions of the seasonal mean precipitation, surface air temperature, geopotential height, zonal-mean wind and zonal-mean temperature agree well with the observations, except for an excessive amount of global precipitation, and warm bias in the tropical upper troposphere. This model improves the representation of regional-scale phenomena and local climate, by increasing horizontal resolution due to better representation of topographical effects and physical processes, with keeping the quality of representation of global climate. The model thus enables us to study global characteristics of small-scale phenomena and extreme events in unprecedented detail.