Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
January 20, 2015 Volume VII ! Tornadoes are an atmospheric event. A tornado is a rapidly rotating column of air known as a vortex that has reached the ground. It is often associated with a funnel cloud, a funnel-shaped cloud that may appear near the ground in a thunderstorm. Tornado winds swirl at speeds that may exceed 300 miles (480 kilometers) per hour on rare occasions. The most damaging tornadoes form in storms called supercells. A supercell is a large, powerful thunderstorm. It contains a rapidly rotating air mass called a mesocyclone. For a supercell to form, and perhaps spawn a tornado, several basic conditions must exist. There must be an adequate supply of moisture to feed the storm. There must be a layer of warm, moist air near the ground and a layer of cool air above. Finally, the winds at higher elevations must differ from those at lower levels in speed, direction, or both. ! ! The deadliest tornado in U.S. history was the Tri-State Tornado of 1925, also called the Great TriState Tornado. A catastrophic storm that traveled from southeastern Missouri through southern Illinois and into southwestern Indiana on March 18, 1925, the storm completely destroyed a number of towns and caused 695 deaths. The Super Outbreak of 2011 was a series of tornadoes on April 26–28, 2011, that affected parts of the southern, eastern, and central United States and produced particularly severe damage in the state of Alabama. It was the largest outbreak of tornadoes ever recorded; preliminary estimates suggested that more than 300 tornadoes occurred across 15 states. The number of deaths caused by the outbreak was, according to initial estimates, at least 340. The states affected were Mississippi, Alabama, Florida, Georgia, South Carolina, North Carolina, Tennessee, Arkansas, Missouri, Virginia, West Virginia, Maryland, Indiana, Ohio, and New York. The first requirement for tornadoes is moisture. Tornadoes and other severe storms often form along a dry line. In North America, the dry line is a boundary separating warm, moist air from the Gulf of Mexico and hot, dry air from the west. The second requirement for tornadoes is air temperature. If there is warm and moist air at a lower altitude and very cold and dry air at a higher altitude, the warmer air will rise rapidly. The air cools as it rises. The faster the wind speed, larger and more violent the storm and the more likely it will spawn a tornado. Storms may develop when warm air rides up over a shallow layer of cooler air. Storms may also form when moist air lifts over mountains, hills, or other high spots. The third requirement for tornadoes is wind. Winds at higher elevations differ greatly from winds at lower elevations. Those things maybe speed, direction, or both. The difference of wind direction and wind speed is called wind shear. Wind shear makes the column of rising air begin to rotate. At first, the swirling air forms a broad, horizontal tube. As the storm develops, the tube tilts upright. It becomes the rotating column of air called a mesocyclone. Most tornadoes form in supercells. But others form in a large group of storms called a mesoscale convective system (MCS). What mesoscale means is between small and intermediate. The MCS is the large group of storms that can cause severe damage. When are tornadoes most likely to occur? ! Tornadoes can occur at any time of the year and day. In the southern part of America, peak tornado season is from March through May. Peak times for tornadoes in the northern part of America are during the summer.A couple of tornadoes in the southern part of America has a second peak time for tornado outbreaks. It is in the fall. During a Tornado If you are at home during a tornado, go to a basement of interior room underground like a bathroom or closet. If you can, get under a sturdy piece of furniture, like a table. Get out of vehicles. Never try to outrun a tornado in your car. Leave it immediately. If you’re outside, go to a ditch or low lying area and lie flat in it. Stay away from fallen power lines and stay out of damaged areas. ! ! If You Are At School During A Tornado If you are at school during a tornado, go to a basement. Basements offer the best protection. If your school doesn’t have a basement, go to interior rooms and hallways on the lowest floor which are away from windows. Get down on your knees and protect your head with your arm. ! !