To Understand A Weather Pattern, Know About Air Movement

by Eric Slarkowski

To understand a weather pattern, no matter where in the world it might occur, it is necessary to know about the interaction of the sun with the Earth, its atmosphere and the air masses that move around the globe. Much of the weather change that we experience on Earth is caused by, or includes, the uneven heat distributed throughout the atmosphere. If the sun heated the land, the oceans and the air at the same level all over the world, there would be no need for the atmosphere to attempt a state of equilibrium.

Simply stated, weather forecasts look at how warm air masses and cold air masses interact, even collide, to create certain conditions. For example, warm air will rise until it comes in contact with a boundary called the tropopause. This is basically a level separating the troposphere and stratosphere that warm air cannot break through.

When an air mass bumps against this barrier it generally spreads in the direction of the poles. As the air cools it moves back toward the Earth at about 30 degrees latitude north and south of the equator. The drop of such an air mass usually results in an area of high pressure, with its common clear skies and little or no precipitation.

While it is not easy to predict weather, over the years meteorologists and other scientists have discovered that the sinking air mass 30 degrees from the equator pushing out whatever air mass is there. The displaced air returns to an area closer to the equator and to low pressure. Sailors have given this air movement the name "trade winds." Eventually the movement of the air mass loses its steam and the "dead" areas around the equator at this time were known as doldrums. The label for this general type of air movement is Hadley cell, because George Hadley, a scientist from England, first described the phenomenon in the 1700s.

But some of the air at the equator rises and, instead of dropping back toward the ground 30 degrees north or south of the equator, continues on toward the North Pole or South Pole. Even the strongest air mass won't always make it all the way to one of the poles, however. The warmer air comes into contact with much cooler air at about 60 degrees north of the equator and south of the equator. Thus the name "polar front."

In this case, the warmer air rises above the polar air mass and much of it makes a return trip toward the equator. The air mass may then sink toward the Earth at the 30 degrees latitude mentioned earlier. This weather phenomenon, called Ferrel cells, was first identified by William Ferrel about 150 years ago. In a slight twist on all this air mass movement, some air does continue on to the North Pole or South Pole, cooling and dropping to the ground, then moving toward slightly warmer climes at 60 degrees. This subset of air movement is known as a polar Hadley cell. Figure in the effect of the earth's tilt and rotation with the movement of air masses and you have most of the ingredients for weather change.

About the Author

Eric Slarkowski writes largely for http://www.alicante-spain.com , a web publication about weather forecasts . On his site one might find out more about his contributions on weather forecasts and murcia weather.