Tornadoes are natural disasters. The United States annually arose from 1000-2000 tornadoes, with an average of five per day. Moreover, tornadoes in America are not only many in number but also large in intensity. For example, on April 3 1974, there was a very strong tornado in the southwestern part of Chicago 89 km. Within two days of appearing 148 times, assets lost about 500 million dollars, killing 315 people.
It is easy for a tornado to appear in the US because of its geographical location, climatic conditions, and weather conditions.
America is bordered on the East by the Atlantic Ocean, to the West by the Pacific Ocean, to the South by the Gulf of Mexico; steam was constantly flowing from the East, West, and South into the United States. There is a lot of water vapor, and thunderstorm clouds are easy to form and develop. When these clouds reach a certain strength, a tornado will be produced. According to statistics, in the US, most of the continent’s states have had this wind.
The United States is predominantly mid-latitude; spring and summer are often subject to tropical high-pressure, although its boundary often influences autumn and winter. The western border area of the sub-tropical high pressure is the converging convection area that rises very strongly, continuously blowing warm and wet air from the Atlantic and the Gulf of Mexico into the United States. That is the additional condition to produce thunderstorms. Thunderstorms are constantly developing rapidly, so a tornado is born.
Tornadoes in the US are most concentrated in the Midwest, most of which appear in spring. According to statistics for the last 29 years, out of two thousand tornadoes in America, about 54% arose in the spring, of which on April 3 appeared 235 times.
In May, the subtropical high pressure dominated the United States in the West just in time for the bar to stop in the Midwest; at that time, the southeast wind brought a large amount of warm and humid air from the Gulf of Mexico. South to the north, there is strong convection up and down in the air with a lot of water vapor, so thunderstorms develop rapidly, thus forming many tornadoes.
In June, a large amount of warm and humid air moved north to Nebraska state. In July, a department moved to Canada, then the number of tornadoes in the US decreased significantly. The tornado’s second route is from southwest to northeast, from western Arkansas through northwest Missouri to central Indiana. These two regions have a concentration of tornadoes because the warm, wet air flowing from the Gulf of Mexico encounters the strong upward movement of the subtropical high pressure that causes.
Here it is necessary to emphasize that, according to statistics of the last 50 years, the number of tornadoes arising in the US has increased by 35 times. Sometimes there are no thunderstorms but also a tornado. This special wind called cloudless tornado occupies about half. How is this strange phenomenon formed?
Some scientists, by curiosity, have researched and investigated. This phenomenon is closely related to the increasing number of cars on the road. On the US’s main roads, there are usually no less than two million cars in operation, more than 60,000 trucks run around the clock. Traffic in the United States follows to the left, each time two high-speed cars avoid each other, forming a counter-clockwise vortex of air. Combined swirly, the air of millions of cars will form extremely powerful vortices. When faced with favorable weather conditions, such as high temperature and humidity, those swirling zones create a tornado.