Investigation on the generation and evolution mechanisms of tidal wave, tornadoes and building damages associated with the "Typhoon 9918"

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A typhoon named 'Typhoon 9918' attacked Japan in late September, 1999. It recorded the maximum instantaneous wind speed of 66.2m/sec (informally 83.9m/sec at Kashima in Kagoshima Prefecture) and caused extensive damages. The number of completely- and half-destroyed houses was 1,300 and the total number of house damage including partly-destroyed one amounted to more than 30,000. It was characterized by the tidal wave due to the strong wind from which the death toll climbed to 19 in the coastal region of the Yatsushiro Sea. In addition, Tornadoes broke out in concurrent with the typhoon in City of Toyohashi and its surroundings located about 700km east from the center of the typhoon, and more than 300 pupils were injured either seriously or slightly.The present research project was aimed to disclose the generation and evolution mechanisms of the tidal wave and tornadoes associated with the typhoon and the mechanism of the house damage due to the strong wind. At first, records on the typh … More oon and meteorological paremeters and the associated tidal wave, tornadoes and damages of buildings and seawalls were collected and analyzed to reveal the mechanisms of generation and evolution of these severe storms and damages. Secondly, numerical simulations were made for the typhoon and the associated tidal wave and tornadoes.As to the tidal wave, the data analyses, together with the numerical simulation and comparison with the case of the 'Typhoon 9119' that took almost the same path, revealed that the strong wind over the large surface area (about 700kmィイD12ィエD1) and the low pressure driven by the typhoon along the worst path and the shallow depth of the Yatsushiro Sea generated and maintained the tidal wave, which conspired on the diurnal high tide of autumn tide, and caused flooding over the seawall and severe damages. In addition the narrow back end of the sea straitened by reclaim also contributed to amplify the tidal wave, that is, deformation of the seabed topography and coast line is also the reason.As to the tornadoes, it was shown that the numerical model can predict successfully the generation and persistence of the mesoscale cumulous convection and thunderstorm with very high vorticity, and so the possibility of the tornado formation. In Japan the tornado forecasting system has not be established. However, the present study suggested the possibility of the tornado forcasting. Less