A Numerical Simulation of a Tornado using WRF

Meteorological statistics show that 20 tornado events occurred per year in Japan. Although most of them are rated F2 or less on the Fujita scale, about 400 residential buildings are partly damaged or completed destroyed due to these tornadoes every year in Japan. Reducing these damages from the meteorological events is highlighted in the building design. It strongly requires better understanding of tornado flow field, tornado-induced wind load and wind pressure distribution acting the buildings in the urban atmospheric boundary layer near the ground. In this study, an analysis of meteorological conditions that led to the F3 tornado event on 6th May 2012 at 0300UTC in Tsukuba city, Japan has been carried out. An attempt has been also made to reproduce the event using the ARW-WRF with NCEP/FNL and JMA/MSM datasets as an initial data with grid nesting method. The simulated meteorological parameters, such as relative humidity, sea level pressure, air temperature and wind velocity time series are favorable for the tornado occurrence and agree reasonably well with the observation results. As a preliminary study, the meteorological parameters have been adopted in 1-way coupling into a CFD urban area model with high mesh resolution in the urban atmospheric boundary layer near the ground. CFD using LES has also been conducted to the model to investigate the effect of the tornado over the urban area in relative comparison with the building damages obtained from the disaster investigation.