Bimodal Distribution of Precipitation Found in the Multimodel Climate Prediction over Central Japan in Winter

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Large-scale trends related to the precipitation in central Japan were investigated in the Coupled Model Intercomparison Project 5 dataset. In the Representative Concentration Pathways 4.5 projections, surface temperature over central Japan increases by 1 to 4 K during the 21st century in most models. Focusing on the trend of surface-air temperature and precipitation in central Japan, these models were categorized into two groups: The precipitation significantly increases in 11 models (group A). On the other hand, the trends of precipitation are small in the remaining 20 models (group B). Analyses of high-frequency components based on daily data revealed that the difference in the precipitation prediction is associated with that in the storm activity around Japan. Relatively enhanced meridional surface-air temperature gradient in the subpolar region may contribute to reinforced storm activity. On the other hand, the zonal surface pressure gradient associated with the Siberian high and the Aleutian low is not strengthened in group A. The climatological wintertime monsoon does not appear to contribute to the difference of precipitation trend in central Japan between the two groups. Moreover, the influence of any other planetary-scale variations is not implied.