Tornadoes are one of the most violent and spectacular meteorological manifestations. They appear suddenly without any warning, they move rapidly leaving a trail of devastation and equally rapidly they disappear into thin air. Tornadoes are characteristic in the Southern part of the United States, in a belt between Texas and Dakota. Every year approximately 1,000 tornadoes hit North America. Generally the energy of a tornado is exhausted in a few minutes, but in 1917 in Mattoon-Charlestown a record tornado lasted over 7 hours and travelled 420 km before it died out.
In fact with such a vast number of events to study, one might think that the phenomenon is one of the best known and best understood. It is not so in reality. Due to the unpredictability of the phenomenon and its rapid evolution, a tornado is actually a very difficult event to study. It can appear at any time, without any warning, and evolves so rapidly that often it disappears even before it is possible to draw close to it to examine it. Furthermore, its manifestations are generally so violent that they can destroy any measurement instrumentation that they come into contact with.
In the USA there is a truly special category of meteorologists , the “tornado chasers” who chase tornadoes. These are professional meteorologists, however there may also be enthusiastic amateurs, fascinated by the spectacular nature of these phenomena. With specially equipped vehicles, provided with TV cameras, anemometers and other meteorology instruments, the tornado chasers move continually on the territory, searching for tornadoes that are forming. Once they identify the event, they follow it, filming and documenting all the stages, carrying out measurements and recording observations. They keep in contact with one another through a constant information exchange network.
For many, it is not only a matter of scientific observation : there are also associations of “enthusiasts” who follow tornadoes to feel the thrill of reaching as close as possible to one of the most destructive and spectacular displays of the atmosphere, in a high-adrenalin “game” that surely is also very dangerous.
Whichever the motivations that inspire the tornado chasers, the observations recorded by these very particular meteorologists are very precious in order to understand a phenomenon that is so difficult to study. In fact it is only since a few years that the Doppler radar techniques have enabled meteorologists to measure the speed of the winds of a tornado more precisely.