Because warm air is lighter, it rises while cold air moves down to take the warm air's place. This circular movement of air is called a convection current. Where the air rises, there's higher air pressure; where it falls, the pressure is low. Since cooling air can't hold as much water vapor as warm air can, the result may be rain, whether as a simple summer thunderstorm or a big hurricane.
A cyclone is a weather system where the air rushes into a low-pressure area, and winds rotate inward in a counterclockwise direction. Cyclones can be very powerful and destructive. A tornado is a very intense, small cyclone. As the very fast winds spiral inward and upward they can pick up large objects like trees, trucks and even rooftops.
The most powerful storms of all are called hurricanes (in Asia they are called typhoons). These huge cyclones can cover hundreds of square miles. Formed over warm tropical oceans, hurricanes can have winds of more than 125 miles per hour. These storms can cause incredible damage due to floods, waves, rain, and wind.
Hurricanes are
A
not created by air masses.
B
formed over arctic oceans.
C
a kind of cyclone.
D
less powerful than tornadoes.