What is a Tornadoe?A tornado is atmospheric storm which consists of rotating column of air which extends down from cumulonimbus cloud (thunder storm cloud). They are usually only small in size and only last for a short period of time. They are often linked with supercell thunder storms.
How are Tornadoes formed?They form because of the interaction between warm air and cold air. They are always formed over ground as the heat from the ground warms the air making it unstable through the day so that it rises. When it rises forms a cumulonibus cloud which coverges with the colder air. The air is then deflected by the Coriolis force and it spins upwards. This rotation is then aided by the differing wind speeds and direction at differnet altitudes. Supercell Thunderstorms are best at creating tornadoes due to there strong upward movement and imense downdraught. Near the rear of the storm a funnel of air can begin to appear which can lower and touch the ground forming the tornado.
Where do tornadoes appear?They are mostly seen in the middle latitudes but can also be linked with the updraught created by large hurricanes. The USA is one of the most common places for tornadoes to form with over 75% of the worlds recorded tornadoes being in this area. This is due to the interaction between the warm air from the south over the Gulf of Mexico meeting with the colder air from the Arctic making perfect conditions for the formation of tornadoes. They have become so common in the southward stretch between Nebraska and Texas that the area has been named "Tornadoe Alley".
What effect do Tornadoes have?Damage caused by tornadoes is often due to the high wind speeds which can reach over 500km per hour. There is also the lifting force of the funnel whcih can move large objects. They also create large preasure differential between the outside of buildings and there inside which can lead to them exploding outwards creating large ammouts of debriswhich does large ammounts of damge as it is blown around.
Acces to geography - Hazards - by Malcolm Skinner (pages48 to 51)
Natural Hazards - by Edward Bryant (pages 93 - 96)