Eng. Abdulwahab Al-sayed

In year 1974,A Twister struck Oklahoma and Arkansas in the United States. More than 320 people were killed, and hundreds were injured. In year 1979, another twister struck the Dominican Republic in the Caribbean Sea, Killing 1100 people, and displacing 150000. Twisters are Known as the most violent and destructive type of storms. There are two types of twisters, hurricanes and tornadoes. A hurricane is known as a very deep depression. Tornadoes have the same definition, but they are much smaller, much more powerful and destructive. Being only a few hundred meters across, the air moves round the central core very fast, some times as fast as 315 Kilometer per hour.

These fast rising winds have the power of uprooting trees, demolishing buildings, and even picking up cars and flinging them several hundreds meters.

The destruction of buildings occurs when a tornado passes over a building and starts sucking up the air from around the building. This makes the pressure on the outside of the building much lower than that on the inside, and that makes the building explodes. The storm may move along it is path at 50 Kilometers per hour and is usually accompanied by lightening, thunder and torrential rain. Tornadoes are particularly destructive when they occur in groups, moving across a city together and leaving a tremendous destruction behind them. Before a tornado starts, large thunder clouds appear in the sky, one area of the clouds becomes extremely dark and dense, after that, the air in this area starts rotating very quickly. Almost a funnel shaped cloud beings to form and extend downwards.

When the funnel reaches the ground level, it raises a great cloud of dust and some other materials.

When a tornado occurs over water, it is known as a water spout. However, the spouts are not formed of water sucked up from the abyss as many people think (except at the very base of the water level), but from water which has condensed out from the damp air lifted from near the sea.

Tornadoes usually occur in quite large numbers in areas around the gulf of Mexico where the atmosphere is very unstable as warm humid air meets cold polar air.

History is full of disasters where caused by tornadoes beside the two incidents mentioned above. In 1965,371 people were killed and more than 3000 were injured, when a series of 37 tornadoes moved across the states of Iowa, Wisconsin, Illinois, Indiana, Michigan and Ohio in the United States. A School with 85 students inside was demolished and the students were carried 137 meters before they were safely returned to the ground, which was considered a miracle for all the students to net be at least injured. In another case, five railway coaches, each weighing 700 tons were lifted from their track, one was carried 24 meters.

Despite all the studies where made about tornadoes, scientists are still not sure how twisters form.

Many theories tried to explain how twisters form, one theory is tat when the layers of the atmosphere are unstable, small eddies which occur commonly near the ground can become magnified, growing stronger as they become larger. Air probably moves down wards, and that would explain why there is very little dust in the center of the tornadoes. Nowadays, it is quite easy to predict and monitor hurricanes. On the other hand, it is difficult to predict tornadoes.

Reference: Beatona Magazine - Environment Public Authority - issue No. 5