A Climatology of Tornado Parameters in Japan Assessed by Dynamical Downscaling Using a WRF Regional Climate Model: Detailed Analysis with Combined Parameters and Preliminary Discussion on Effects of Future Climate Change

This study updates our previous study that investigated a climatology of tornado parameters in Japan. Tornado classified as significant (F3-F5 damages) are considered for the purpose of the regionalization of tornado intensity for use in the engineering design of infrastructure. The method of analysis is based on evaluating the frequency of exceeding a threshold value of a tornado parameter with a high-resolution (the horizontal resolution of 5 km) gridded dataset, in which tornado parameters are calculated on each grid point. A threshold value for each parameter is set from mesoscale analysis of significant tornado events in Japan and the United States using the WRF (Weather Research and Forecasting) model. The earlier attempt for a long-term (50 years stating from FY1961) dataset, generated by dynamical downscaling through applying the WRF regional climate model to the ERA-40 and ERA-interim reanalysis, suggested that the use of traditional tornado parameters such as MUCAPE (Most unstable convective available potential energy), 0-3km SREH (Storm relative Helicity), and EHI (Energy Helicity index) is quite useful in assessing high-impact tornado intensity regions and in understanding of terrain effects. In this presentation, combined tornado parameters including SCP (Supercell composite parameter), STP (Significant tornado parameter), and VGP (Vorticity generation parameter) are tested with a longer-term dataset. In addition to the investigation for the current climate, effects of global warming on the regionalization are discussed. For this, downscaling of future climate has been performed using MRI-AGCM-32S simulation, and near-future climatological dataset (25 years starting from FY2015) as well as another dataset (25 years starting from FY2075) are used in consideration of possible differences in a climatology of significant tornado occurrence found for the current climate.