Text b Tornadoes

A tornado is one of the most destructive natural disasters. The most extreme tornadoes can reach wind speeds of more than 300 mph, stretch more than two miles across, and stay on the ground for dozens of miles.

The main characteristics of a tornado are shape, size, colour and rotation. A typical form of a tornado is a funnel. However, tornadoes can appear in many shapes and sizes. Small, relatively weak landspouts can be visible as a small swirl of dust on the ground. Large single-vortex twisters, often violent, are known as wedge tornadoes or wedges. Tornadoes in the dissipating stage can appear like narrow tubes, or ropes and are called rope tornadoes.

Tornadoes, depending on the environment in which they form, can have a wide range of colors. For example, tornadoes forming in a dry environment can be nearly invisible, marked only by swirling debris at the base of the funnel. Funnels which pick up little or no debris can be grey to white.

Another characteristic of a tornado is rotation. Tornadoes normally rotate cyclonically. Approximately 1% of tornadoes rotate in an anticyclonic direction in the northern hemisphere.

There are at least two scales for rating the strength of tornadoes. They are the Enhanced Fujita and TORRO scale. The Enhanced Fujita scale (EF) rates tornadoes by caused damage from 0 to 5. For example, an EF0 tornado is the weakest one. It damages trees, plants, crops but not substantial structures. An EF5 tornado is of the strongest category. It rips buildings off their foundations and can deform large skyscrapers. The TORRO scale (T) ranges from a T0 for extremely weak tornadoes to T11 for the most powerful known tornadoes.

The United States experiences by far the most tornadoes of any country, and has also suffered the most intense ones. The time of year is a big factor of the intensity and frequency of tornadoes in the United States. On average, in the United States as a whole, the month with the most tornadoes is May, although tornadoes can occur at any time of year. They tend to occur in the afternoons and evenings. Over 80% of all tornadoes strike between noon and midnight. They can happen in groups and destroy the whole city.

Active Vocabulary to Text b

shape	- форма
debris	- обломки
strength	- сила
funnel	- воронка
to rate	- оценивать
to rotate	- вращать(ся)
to vary	- менять(ся)
to occur	- происходить
invisible	- невидимый
powerful	- мощный

Questions on Text b

1. What is a tornado?

2. What is the typical form of a tornado?

3. Could you name other forms of a tornado?

4. What are the main characteristics of a tornado?

5. Does the colour of a tornado depend on the environment where it forms?

6. How many scales are there for rating the strength of a tornado? What are they?

7. The USA experiences the most tornadoes, doesn’t it?

8. Which is the biggest factor of the intensity and frequency of a tornado?

9. Can tornadoes happen in groups?

10. What damage can the strongest tornadoes cause?

MAN-MADE DISASTERS