Estimation of average wind speed and gust factors during the passage of typhoon No. 0423 in a mountainous region in Ehime Prefecture, Japan

On October 20, 2004, Typhoon No. 0423 passed through Shikoku region of Japan between 13:00 JST and 17:00 JST. Approximately 300 greenhouses in a mountainous area formerly known as Kuma-cho in Ehime Prefecture were damaged by the typhoon. In this study, wind conditions generated by the typhoon in this region were simulated using large eddy simulation (LES). The reproducibility of wind conditions was verified by comparing the simulated values with the average wind speed recorded at the Automated Meteorological Data Acquisition System (AMeDAS) observation station in Kuma-cho and gust factors recorded at three wind observation points from 2010 (or 2011) to 2014. The LES was based on a generalized curvilinear collocated grid. For the initial and inlet boundary conditions, Meso-Scale Model Grid Point Values (MSM-GPV) were used. The average wind direction and the wind speed at the AMeDAS observation station were estimated, and the simulated results appeared to be reasonable. Wind gust factors at the three observation points were simulated and compared with the observed data from 2010 to 2014 (or 2011 to 2014). At each observation point, no significant differences were found between the gust factors during October for each year. The gust factors simulated by LES for each observation point were within the range of the measured values. However, wind conditions during the collapse of the greenhouses and fall wind that seemed to affect the collapse could not be reproduced. The results suggest that boundary conditions from an hour earlier than those used in this study should be used and gust factors at high average wind speeds at the three observation points should be verified in order to estimate wind conditions at the time when greenhouses collapsed. Further, temperature field and wind shear should be introduced into this simulation model in order to reproduce the fall wind.