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| Sunday, 28 November 2004 |
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Junior Observer |  |
| News Business Features Editorial
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Gone with the wind Imagine huge dark clouds with strong winds touching the ground during heavy rain and lightning, and animals, vehicles and even houses flying, causing major destruction. This might sound more like a story to you - but people in many parts of the world (especially United States of America) experience this every year due to tornadoes, considered nature's most violent storms. A tornado is a violently rotating column of air extending from a thunderstorm to the ground. Tornado winds can reach 300 miles per hour. This is about five times as fast as a car driving on a highway. They cause damage when they touch the ground. Tornadoes can be categorised as weak, strong and violent. Weak tornadoes often have a thin, rope-like appearance. About seven in 10 tornadoes are weak, with rotating wind speeds no greater than about 110 miles per hour. The typical strong tornado often has what is popularly considered a more 'classic' funnel-shaped cloud associated with whirling updraft. Rotating wind speeds vary from 110 to 200 miles per hour. Nearly three in 10 tornadoes are strong. Weak and even strong tornadoes do not level well-built houses. Thus, a secure home will offer shelter from almost all direct tornado strikes. Only violent tornadoes are capable of levelling a well-anchored, solidly constructed house. Fortunately, less than two per cent of all tornadoes reach the 200 miles per hour or above 'violent' category. Most violent tornadoes only produce home-levelling damage within a small portion of their overall damage path. What causes tornadoes? Thunderstorms develop in warm, moist air in advance of eastward-moving cold fronts. These thunderstorms often produce hail, strong winds and tornadoes. Tornadoes occasionally accompany tropical storms and hurricanes that move over land. Tornadoes are most common to the right and ahead of the path of the storm centre as it comes onshore. There are various types of tornadoes. Some may form during the early stages of rapidly developing thunderstorms. Some may appear nearly transparent until dust and debris are picked up. Occasionally, two or more tornadoes may occur at the same time. How do tornadoes form? First step Before thunderstorms develop, a change in wind direction and an increase in wind speed with increasing height creates an invisible, horizontal spinning effect in the lower atmosphere. Second step Rising air within the thunderstorm updraft tilts the rotating air from horizontal to vertical. Third step An area of rotation, 2-6 miles wide, extends through much of the storm. Most strong and violent tornadoes form within this area of strong rotation. Moments later a strong tornado develops in the area. Tornado myths Myth: Areas near rivers, lakes and mountains are safe from tornadoes. Fact: No place is safe from tornadoes. It can happen anytime, any place in the world. Myth: The low pressure within a tornado causes buildings to 'explode' as the tornado passes overhead. Fact: Violent winds and debris slamming into buildings cause most structural damage. Myth: Windows should be opened before a tornado approaches to equalise pressure and minimise damage. Fact: Opening windows allows damaging winds to enter the structure. The best option is to go to a safe place. **** USA most at risk Although tornadoes occur in many parts of the world, this destructive force of nature occurs most frequently in the United States of America.In an average year, 800 tornadoes are reported nationwide, resulting in 80 deaths and over 1,500 injuries. In America every state is at some risk from tornado damage, but states in the 'Tornado Alley' (Arkansas, Iowa, Louisiana, Minnesota, Nebrasaka, North Dakota, Ohio, Oklahoma, South Dakota and Texas) face the highest risk. Tornadoes can form anytime of the year, but the typical season runs from March to August. |
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