“Wind is the flywheel of the Sun’s heat engine, the motion produced by raw solar energy as it reaches Earth. It sculpts our weather, as it forms clouds, fronts and countless other weather features out of thin air. Yet for a surprisingly long time, people didn’t quite know what to make of the wind.” (Henson, 23).
The source of wind is the sun’s heat. “The radiation from the sun heats the ground. The ground, in turn, heats the air… the air rises. As it rises, cooler air comes in to replace the rising air; what we feel as wind. The faster the air rises, the faster the wind blows to take its place. Every time will feel the wind, regardless if is from the north, south, east, or west, somewhere else around the world the wind is rising.” (www.noaa.gov)
The wind’s direction and effect on the weather is determined by pressure systems and fronts. There are two different types of air pressure that effect the weather, they are high pressure areas and low pressure areas. These two things both have different types of wind in and around them. High pressure areas are like a mound of air sitting over a particular area. The winds cascade downward and outward from the high pressure area in a clockwise motion in the Northern Hemisphere and a counterclockwise motion in the Southern Hemisphere. Lows are just the opposite, the air is drown inward and around the low pressure area in a counterclockwise motion in the Northern Hemisphere and a clockwise motion in the Southern Hemisphere.
There have been many different schools of thought about where wind comes from and how it is created over the centuries but the theory of wind that is used in today’s weather forecasting is based on the “frontal theory” come up with by a group of Belgium scientists lead by Velhelm Bjerknes in the 1920s.
The frontal theory was based on the Earth’s atmosphere being fluid. This group took the idea of discontinuity, such as vinegar separating from oil in a jar of salad dressing, and applied it to weather. “They named these sharp boundaries of pressure and temperature “fronts”, and labeled them as warm or cold, based on whichever air mass was advancing.” (Henson, 25).
“Fronts are bands of lower pressure that arc outward from low-pressure centres. Each front serves as a dividing line between highs of different atmospheric qualities.” (Henson, 26). The air masses are moved across the land and water by the winds created in and around them by the rising and falling air. When the two air masses collide in a front it creates different weather depending air temperatures and moisture levels creating the fronts.
Henson, Robert. A Rough Guide to Weather. London: Rough Guides. Ltd., 2007
www.noaa.gov
