Regional Climate Projection Experiments on the Baiu Frontal Activity around the Japan Islands Using a Non-Hydrostatic Cloud-System-Resolving Model

Abstract

Regional climate experiments focusing on the Baiu frontal precipitation were performed on the Earth Simulator using a non-hydrostatic cloud-system-resolving atmospheric model (NHM) with a horizontal resolution of 5 km (5km-NHM) and 1 km (1km-NHM). The outputs of an atmospheric general circulation model (AGCM) with a horizontal resolution of about 20 km were used as the boundary of 5km-NHM. The time-slice method in both the present and future climates was applied for the experiments of the AGCM and NHM. In the present climate experiments, it was evaluated that the precipitation distribution and precipitation frequency spectrum (PFS; frequency with intensities) of the 5km-NHM were well reproduced in comparison with those observed. Here, the AGCM in the present climate well reproduced the large-scale characteristics of the Baiu frontal precipitation. The Intergovernmental Panel on Climate Change (IPCC) A1B CO2 emission scenario was used to project changes in the precipitation property around the Baiu front due to global warm- ing in the future climate around the end of the 21 st Century. The 5km-NHM projects not only an increase in precipitation around Western Japan associated with the elongation of the Baiu front due to global warming but also an intensification of precipitation associated with the enhancement of the convectively unstable strat- ification. The 1km-NHM experiment demonstrates the effects of the high resolution and shows further quality improvements of the PFS and higher reproducibility of extreme precipitation events associated with the organizations of convective systems than the 5km-NHM experiment.