Destruction mechanism of Oklahoma Tornadoes in 1999

概要

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On the trace of a devastated zone by a tornado we often catch a strange sight that a heavily damaged house is adjacent to a sound house and a partial half of a roof is lost leaving the last half perfect Also tales on persons who were flying through the air and softly landed l00 yards away are heard about. These phenomena are hard to be understood without the small but strong vortexes which exist in a large rotational stream in diameter of the funnel cloud. ln the evening of May 3 in 1999, Oklahoma State was attacked by 62 tornadoes killing 42 people. Articles from the newspapers and the video tapes from the television stations were analyzed and arranged in time sequence. A scene of falling thick debris in the KFOR-TV video aided in associating a surface friction model that consists of many child vortexes with axis slanted to the current direction in the parent vortex. This flow system brings destructive power in the right side of the proceeding direction with two actions ; one is stretch of the child vortexes and the other the concentrated down draft. If this idea is applied to the disaster by the tornado running 24 miles from Bridge Creek to Midwest Cily, there can be found a general tendency that the fierce action of small vortexes was more remarkable in the earlier stage and the gusty downdraft was developed in the later slage. A downburst disaster was identified at Stroud 40 miles apart from the main tornado site.
日本自然災害学会の論文