Future atmospheric surface circulations and their impact on the regional climate of Japan based on the CMIP6 projections and observed statistics

抄録

Future changes in sea-level pressure (SLP) around Japan are investigated using the Coupled Model Intercomparison Project phase 6 (CMIP6) projections, and their impacts on future regional change of surface air temperature and precipitation, including their extremes, are estimated based on observed statistics. The SLP patterns around Japan are quantified by defining a surface wind index, and are compared with the CMIP5 projections, revealing a similar mean change but a reduction in inter-model uncertainty. The future seasonal cycle represented by the index indicates that the spring SLP pattern will appear earlier, but the autumn pattern will be delayed. The CMIP6 models projecting stronger winds from warm (wet) areas tend to simulate a warmer (wetter) future climate over Japan, which is consistent with the statistical relationships in observations. The impact of future SLP changes on regional climate is assessed using the index based on observed relationships. The results indicate that future westerly anomalies (relative to the present day) in summer will increase mean precipitation on the Sea of Japan side of eastern and western Japan, but decrease extreme precipitation on the Pacific side of eastern Japan. The southerly anomalies in winter and autumn will increase mean and extreme precipitation over western Japan.