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龙卷风是自然界最猛烈的风暴之一。大多发生在3月——5月份之间，贯穿整个春季和夏季，以落基山脉地区最为频发。通常伴有雷电和暴雨,龙卷风形成于干线,是由于冷热空气碰撞而改变风向和风速，增加低层大气水平方向的风俗，空气上升，使垂直的空气旋转倾斜。(美国国家海洋和大气管理局,1992)。
这种运动就会引起龙卷风,以藤田分级评定其强弱。此外,大多数被评定为弱的龙卷风通常规模为F0或者F1。这些龙卷风相比较而言造成的损失最小，风速高达每小时110英里，持续时长为十分钟。强大的龙卷风规模大概为F2、F3或F4,风速在每小时110和205英里之间的。他们持续的时长为20分钟或更长。F5是最为暴力的龙卷风，死亡人数最高和伤害最大。他们的时长至少一个小时或更长时间，风速超过每小时205英里。(美国国家海洋和大气管理局,1992)龙卷风随时可能发生,可能造成损害。每个龙卷风都有额定的藤田分级所评定的规模。
Tornadoes are one of nature's most violent storms. The majority of them occurs east of the Rocky Mountains during the spring and summer months, March through May. Usually accompanied by thunderstorms, tornadoes form on the dry line, where hot and cold air fronts collide, and a change in wind direction and increase in wind speed with horizontal spinning in the lower atmosphere and air rises with updraft tilts to rotate the air to vertical (NOAA, 1992).
This movement causes tornadoes that are rated weak or strong on the Fujita Scale. Moreover, the majority of tornadoes are classified as weak, which is either an F0 or F1 on the scale. These tornadoes have the least amount of damages and can have winds up to 110 miles per hour with a lifespan of one to ten minutes. Next, strong tornadoes, F2, F3, or F4, have wind speed between 110 and 205 miles per hour. They have a lifespan of up to twenty minutes or longer. Last, F5 or violent tornadoes have the highest death count and do the most damage. They have a lifespan of at least an hour or longer with winds greater than 205 miles per hour. (NOAA, 1992) Tornadoes can occur at any time and can cause damages. Each tornado is rated on the Fujita scale. GIS Technologies
GIS technology is used to better understand tornadoes. It is used to predict possible tornado damages. GIS helps assess damages done by tornadoes. It keeps tracks of the different paths and maps historical references of tornados. GIS is used to help people that have been in or want to avoid tornadoes.
GIS is used to predict possible damages done by tornadoes. ESRI developed a what-if scenario to evaluate possible tornado damages for the Metroplex in Oklahoma. According to ESRI:
The North Central Texas Council of Governments (NCTCOG) and the National Weather Service in Fort Worth have put together a Tornado Damage Risk Assessment, which estimates the results of multiple scenarios in which the Oklahoma tornadoes are transposed across the Metroplex.
Oklahoma tornadoes' damage paths were laid over the geographical data and had actual damage contours from powerful tornadoes that were mapped with ArcInfo. It projected possible tornado paths of slightly north-south and east-west across the Metroplex. ArcInfo showed the geographic processing engine, and ArcView GIS mapped and manipulated data for effective results. ArcView 3D Analyst constructed models and animations to show the area's vulnerability to violent tornado tracks. ArcInfo took data such as appraisal records, land use classification, demographic centers, and aerial photography merged it into records and overlaid it with the tornado paths. (ESRI, 2001) ARC GIS used this information to estimate the potential damage costs in the area to help realize the importance of preparation and good advance warning and help keep people aware of the potential dangers and threats. ESRI what if scenario helps keep people aware of the dangers of tornadoes.
GIS is used to assess damages done by tornadoes. Pictometry International Corp., a leading provider of geo-referenced aerial image libraries, used new aerial oblique imagery of areas in the south that were hit by tornadoes. This information was given to counties to help assess damages and captured more than 140 square miles of imagery in Mississippi and Tennessee counties after storms hit (Pictometry). With a quick response time, this imagery helped officials to accurately view and assess damages both before and after the storms. GIS has helped Pictometry International Corp. assess areas damaged by tornadoes.
People can track tornadoes through tracking, mapping and historical referencing tornadoes. One can see where different tornado paths struck through web interactions. The website, http://climate.engin.umich.edu/tornadopaths/, allows the user to fly and see the different paths. Also, different facts are given about these tornadoes. In addition to tracking, companies map tornadoes and historical references. Companies use these maps to assess the possibilities of tornadoes in given areas. These maps are categorized by the strength of the tornadoes. FEMA keeps track of where different tornadoes hit on its tornado distribution map. They use GIS to compile data to analyze tornado data. Tornadoes can be tracked and be kept for historical referencing.
.GIS technology is used to compile different sets of data for tornadoes. It is used to predict possible tornado paths and damages. GIS is used to estimate damages of actual tornadoes. Technology is used to have tracking interaction as well as keeping track of where tornadoes hit. GIS is becoming more readily available to help those in disaster areas. Trends
Each state has its own trend. Pennsylvania has the majority of tornadoes in the east and west sides of the states. Ohio has the most tornadoes all over the state. West Virginia has the least amount of tornadoes but have three big areas of tornadoes. These trends play a role in where tornadoes most likely occur due to landscapes and locations.
Due to the landscape, tornadoes occur all over Pennsylvania. It has most of its tornadoes in the east and west sides of the state. There are not as many tornadoes in the center of the state or in northeast or southwest corners of the state, which has between 0-10 or 10-20 tornado events per square mile since 1950-2002 (PASC). The areas that have the most tornadoes are southeastern especially Philadelphia county and surrounding counties, as well as Beaver and Lawrence Montour counties. Philadelphia County has the most in the state with 50-60 tornado events per square mile between 1950-2002. (PASC). The rest of the state has a moderate amount of tornadoes. These trends coincide with the landscape.
The location of Ohio plays a huge role on the amount of tornadoes it receives. The western part of Ohio is in the Tornado Ally of the United States. Ohio averages about 10 tornadoes a year with an average of 16 tornadoes a year (2001 Ohio Insurance Facts). Counties in southwestern part of the state that touch either Kentucky or West Virginia have fewer tornadoes with the exception of the counties that touch Pennsylvania. Overall, Ohio has a lot of tornadoes.
On the contrary to Ohio, West Virginia does not have many tornadoes. However, there are areas that are heavily hit by tornadoes. These areas are the tip of eastern panhandle, northern West Virginia near the Pennsylvania border, and in the southeast and southwest close to the Virginia, Kentucky and Ohio borders. Central, southern, and northern panhandle have very few tornadoes (WVU extension services). Very little damage is done by these tornadoes. West Virginia has few tornadoes a year.
Pennsylvania, Ohio, and West Virginia have different trends due to locations and landscapes. Ohio has the most tornadoes in the tri-state area, and West Virginia has the least. Tornadoes occur in all three states with different forces. Tornado Outbreaks:
There were two major tornado outbreaks in the tri-state area. The first one affected Pennsylvania. The other one occurred on April 3-4, 1974 and was one of the biggest tornado outbreaks in the United States. Ohio and West Virginia was hit hard during this time. These tornado outbreaks did a lot of damage and harmed many of people.
On May 31, 1985, tornadoes hit in Pennsylvania. There was a collision in the air masses over Ohio and Southwestern Pennsylvania. Theses storms formed very quickly and there was little warning that these storms were coming. There were already tornadoes forming when warnings were issued. According to the Pittsburgh Post-Gazette, “There was a line of violent storms, a total of 17 tornadoes. These storms left 65 dead, destroyed 1,009 homes and caused an estimated $375 million in damage in western PA.” These storms caused great damages to those involved.
One of the biggest tornadoes outbreaks occurred on April 3-4, 1974. This outbreak occurred due to the right atmosphere pressures. In the tri-state area, Ohio and West Virginia were affect by this storm. According Tornado Super Outbreak, “In Ohio, these storms killed 41, injured 2,000, and damaged about 7,000 homes.” The hardest hit area was Xenia, Ohio. Here was one of the most intense tornadoes of the outbreak that left 30 dead, more than 1,100 injured, and over 1,000 homes destroyed (Tornado Super Outbreak). A similar experience occurred in West Virginia in the pre-dawn hours on April 4 when the storms came through moving eastward. The hardest hit area in West Virginia was south and east of Beckley was struck by several tornadoes. Overall, “thirty-two persons were injured and six people died including a child in a mobile home;” according to Tornado Super Outbreak. This was one of the most deadly storms in the United States.#p#分页标题#e#
These tornado outbreaks did a lot of damaged to properties. The May outbreak did the most damage to the southwestern Pennsylvania. The April outbreaks did the most damage to Ohio and West Virginia. These massive storms are caused by big air mass collisions. Bibliography Carpenter, M. (2005). The day the twister came. Pittsburgh Post Gazette. Retrieved April 28, 2008 from http://www.post-gazette.com/pg/05149/511826.stm Edgetech America, Inc. (2008) GIS map gallery: Tornado hits (1950 - 1996). Retrieved April 28, 2008 from http://www.discovergis.com/Map/MapTornado.htm ESRI (2001) Tornado alley “what if” scenario brought to life with gis. Retrieved April 28, 2008, from http://www.esri.com/news/arcnews/spring01articles/tornado-alley.html FEMA (2006). Historical tornado distribution map (1950-1995). Retrieved From April 28, 2008, from http://www.fema.gov/plan/prevent/saferoom/maps_torn_distr.shtm. Ohio Insurance Institute (2001). Tornadoes in ohio and us. Retrieved April 28. 2008, from http://www.ohioinsurance.org/factbook2001/chapter4/chapter_4m.htm PASC (n.d.). Tornadoes. Retrieved April 28, 2008 from http://pasc.met.psu.edu/PA_Climatologist/extreme/Tornado/PEMA_tornado.html Pictometry (2008) Oblique Imagery from Pictometry's Economic Alliance Partnership Helping Tornado-Struck Counties Assess Damage. Retrieved April 28, 2008, from http://www.gisdevelopment.net/news/viewn.asp?id=GIS:N_hyaxeskdvw Samson, P. (2007). Fly tornado paths using google earth. Retrieved April 28, 2008, from http://climate.engin.umich.edu/tornadopaths/ Tornado Superoutbreak (n.d). April 3, 1974. Retrieved April 28, 2007 from http://www.april31974.com/county_damage.htm U.S. Department of Commerce National and Atmospheric Administration (1992). Tornadoes… Nature's most violent storms Retrieved April 28, 2008, from http://www.nssl.noaa.gov/edu/safety/tornadoguide.html. U.S. Department of Commerce National and Atmospheric Administration (2007). Enhanced f scale for Tornado damage. Retrieved April 28, 2008, from http://www.spc.noaa.gov/faq/tornado/ef-scale.html.. U.S. Department of Commerce National and Atmospheric Administration (2006). April 3, 1974 superoutbreak. Retrieved April 28, 2008 from http://www.crh.noaa.gov/ind/april31974.php WVU Extension Service Disaster and Emergency Management Resources (n.d.) Tornadoes http://www.wvu.edu/~exten/depts/cewd/wvdemr/Disaster%20&%20Emergency%20Management%20Resources%20(PDF |
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