Education Links
Leaving Cert
Maths
French
English
Chemistry
Physics
Biology
Economics
Spanish
Geography
History
Junior Cert
4. Where do they occur?
Tornadoes form in many parts of the world (including Ireland) but they tend to be concentrated in the interiors of large continents. They are most common in the US, particularly along a narrow corridor extending from Texas toward the north-east termed 'tornado alley'. In the US these storms occur in all months but are most frequent in the spring months (March-June). As spring gives way to summer the locations of tornadoes moves from south to north. In early spring they tend to occur in the southern states but by autumn they may occur in Canada. The distribution of tornadoes within the US is closely tied to its physical geography. If you examine a map of north America you should notice several factors:
1. A landmass that extends over 50o latitude, from tropical
to polar climates.
2. A mountain barrier (the Rockies) extending from south to north along
its western side that prevents mild Pacific air from moving inland.
3. A large pool of warm water (the Caribbean Sea) located to the south.
The severity of storms over North America results from the severe differences
between the types of air found here. In much of western Europe all the
air is derived from the ocean and is mild - the difference between air
from the tropics and that from the poles is relatively small. By comparison,
in North America different types of air are found in proximity to one
another. In spring particularly, three different types of air (cold and
dry, hot and dry, and warm and moist) are drawn together along a narrow
zone termed the dryline, providing the ingredients for severe storms.
Along this dryline, warmer, lighter air is located beneath colder, heavier
air creating an unstable atmosphere. Rapid, explosive, vertical motion
results as the lighter air switches position with the heavier air above.
