Atmosphere Contents

6. Secondary Circulation

Tornadoes are areas of intense low pressure which occur over land

Tornadoes

Although much smaller in size than the tropical cyclone tornadoes can be equally devastating. As with tropical cyclones the formation of tornadoes is not well understood. They seem to form in association with a squall line - a line of thunderstorms that may extend hundreds of kilometres. This type of thunderstorm activity is particularly common over the USA in spring and summer. Consequently, the USA experiences more tornadoes than any other country in the world, averaging 800 per year with an average of 100 people being killed every year.

What are tornadoes and how do they form?