Environment Canada Confirms Tornado Touched Down In Storm
Wednesday May 16, 2007
It wasn’t just their imagination – Environment Canada investigators have confirmed what the locals already know. A tornado did, in fact, touch down in the western part of the province during the height of Tuesday’s violent storm. The F1 twister, the second least severe of all those on the Fujita Scale used to measure their intensity, left a wide swath of damage between Mitchell and Monkton in Perth County, not far from Stratford.
Experts estimate it turned out winds between 120 and 150 kilometres an hour at its most intense moments. Other residents in other places have also reported suspected twisters, but the weather authorities haven’t been able to prove that they actually happened. “The investigation continues, and there have been other reports of wind damage and hail damage, but right now that stands as the only confirmed tornado,” explains Geoff Coulson.
Homes were damaged, trees and power lines were downed and the winds played havoc with the surrounding countryside. But despite the wicked weather, there were no reports of serious injuries or deaths.
source: http://www.citynews.ca/news/news_11069.aspx
Fujita Scale — Rating the Severity of Tornadoes
The Fujita scale is used to rate the severity of tornadoes as a measure of the damage they cause. The scale was devised in 1971 by the Japanese-American meteorologist Tetsuya (Ted) Fujita. It classifies tornadoes using the following scale.
F0 – light winds of 64 to 116 km/hr; some damage to chimneys, TV antennas, roof shingles, trees, signs, and windows and accounts for about 28 percent of all tornadoes.
F1 – moderate winds of 117 to 180 km/hr; automobiles overturned, carports destroyed, and trees uprooted. F1 tornadoes account for about 39 percent of all tornadoes.
F2 – considerable winds of 181 to 252 km/hr; roofs blown off homes, sheds and outbuildings demolished, and mobile homes overturned. F2 tornadoes account for about 24 percent of all tornadoes.
F3 – severe winds of 253 to 330 km/hr; exterior walls and roofs blown off homes, metal buildings collapsed or severely damaged, and forests and farmland flattened. F2 tornadoes account for about six percent of all tornadoes.
F4 – devastating winds of 331 to 417 km/hr; few walls, if any, left standing in well-built homes; large steel and concrete missiles thrown great distances. F4 tornadoes account for about two percent of all tornadoes.
F5 – incredible winds of 418 to 509 km/hr; homes leveled or carried great distances. F5 tornadoes can cause tremendous damage to large structures such as schools and motels and can tear off exterior walls and roofs. Tornadoes of this magnitude account for less than one percent of all tornadoes and have never been officially recorded in Canada. However, recent research suggests that as many as two may have occurred in Saskatchewan, regardless, F5 tornadoes are possible in Canada every summer.
http://www.pnr-rpn.ec.gc.ca/air/summersevere/ae00s12.en.html
藤田级数
藤田级数是一个用来量度龙卷风强度的标准，由芝加哥大学的美籍日裔气象学家藤田哲也于1971年所提出。
等级F0 风速 <73 mi/h <32 m/s 出现几率 29% 受害状况 程度轻微。表现为：烟囱，树枝折断，根系浅的树木倾斜，路标损坏等。 等级F1 风速 73–112 mi/h 33–49 m/s 出现几率 40% 受害状况 程度中等。表现为：房顶被掀走，可移动式车房被掀翻，行驶中的汽车刮出路面等。 等级F2 风速 113–157 mi/h 50–69 m/s 出现几率 24% 受害状况 程度较大。表现为：木板房的房顶墙壁被吹跑，可移动式车房被破坏，货车脱轨或掀翻，大树拦腰折断或整棵吹倒。轻的物体刮起来后像导弹一般，汽车翻滚。 等级F3 风速 158–206 mi/h 70–92 m/s 出现几率 6% 受害状况 程度严重。表现为：较结实的房屋的房顶墙壁刮跑，列车脱轨或掀翻，森林中大半的树木连根拔起。重型汽车刮离地面或刮跑。 等级F4 风速 207–260 mi/h 93–116 m/s 出现几率 2% 受害状况 破坏性灾害。表现为：结实的房屋如果地基不十分坚固将刮出一定距离，汽车像导弹一般刮飞 等级F5 风速 261–318 mi/h 117–141 m/s 出现几率 <1% 受害状况 毁灭性灾难。表现为：坚固的建筑物也能刮起，大型汽车如导弹喷射般掀出超过百米。树木刮飞。是让人难以想象的大灾难。电影《龙卷风》（Twister）中将F5级龙卷风称为“上帝之指”，意指上帝用其手指翻弄地球。总之，其横扫之处无所幸免。 等级F6 风速 319–379 mi/h 142–169 m/s 出现几率 <0.001% 受害状况 程度自己想象吧。表现为：F6级的龙卷风是否存在还未被证实，但是有几份非正式报告指，最近发生的一次出现于1999年奥克拉荷马州的摩尔(Moore)。F6级以上的龙卷风与F5级很难区别。原因在于，当F6级龙卷风最强风速的中心部位还未触及物体时其周围的风速足以将一切物体破坏。此级别的龙卷风发生几率十分稀少。 http://baike.baidu.com/view/529592.htm
