W. J. Rayment / -- Wind on planet Earth is caused by the heat of the sun (the source of most of the energy and movement on the planet). The sun's rays strike the Earth and heat up the air. It is a well known fact that hot air tends to rise (because it is an expanding gas). This is why a hot air balloon will rise. It is why when you open an oven a gush of air seems to come forth. It is why flames from a fire tend to go straight up.
Where the air heats up and rises we have a low pressure area. As the air gets farther away from the surface, it begins to cool. The force of gravity keeps it from shooting into space and the force of more warm air below it makes it move sideways. As it cools, then, it begins to push down on the air below it. The air stacks up, creating a high pressure area. The air at the bottom of this column of cooler air must go somewhere so it feeds into the low warmer area where it gets heated and starts the process all over again. These pressure differences are measured using a barometer.
Over water a new dynamic begins when moist warm air becomes sucked up into the low pressure center and stacks up on itself. With no land, buildings or trees in the way to break up the winds feeding it, the winds pick up speed. The whole structure is set into a swirl by the spin of the Earth. The higher speed of the earth at the equator than at the poles sends winds whirling around a center in a counter-clockwise manner (in the northern latitudes). To see how easy it is to set this dynamic in motion, experiment with a flushing toilet (you can't get it to spin clockwise).
Hurricanes generally begin in their life in the East Atlantic near Africa. (This same phenomena is called a typhoon when it occurs in the Pacific.) They usually start near the equator where there is plenty of warm moist air. They travel eastward (counter to the prevailing weather patterns in the United States). A hurricane-force wind begins at about 64 miles per hour and can work up to speeds in the hundreds. This is sufficient force to sink ships, rip up trees, destroy buildings and make the sea surge (which causes even more damage).
These winds, swirling in a circle, have a central point called an eye. You have undoubtedly heard of "the eye of the storm" used as a metaphor in literature and news articles. It implies that there are tremendous destructive forces all about. Amazingly enough, this center is very calm. Yet, as you would expect, it is under very low pressure.
The scale of hurricanes is generally huge. They can be 500 miles across. They tend to create havoc when they hit land. Hurricane Katrina in New Orleans and Mississippi illustrates what one of these storms is capable of doing. On average, there are about 45 Hurricanes per year. This seems like a lot, but they strike various locals in Eastern America. They also quickly lose their force when the get over land and their supply of water, heat and open spaces all dry up. Even after they are downgraded to tropical storms, they still pack a punch and can cause flooding and destroy crops.
Shuttering Windows for Storms