Weather Facts



What Causes Wind?

Wind is caused by the difference in pressure from one point on the earth's surface to another. The air moving from the area of higher pressure to the area of lower pressure is called wind. The air does not move directly from the point of highest pressure to the point of lowest pressure. The earth's rotation affects the air flow by deflecting it to the right. This effect is called the Coriolis Effect. In the Northern Hemisphere, this causes air to flow clockwise around high pressure areas and counter-clockwise around low pressure areas. Now, you may ask - What causes the difference in pressures on the EarthÝs surface? - The answer to that is quite complex so I won't go into great detail here. Generally, you could say that the cause of the difference in pressure across the globe is the uneven heating of the Earth's surface from the sun. This is due to several factors. Land warms and cools much faster than water. And, of course, latitude affects how much solar radiation is received each day and returned to space each night.. In addition, topography has an effect on solar radiation. Even the types of vegetation affect how much sunlight is absorbed and reflected. Snow cover plays a major role in absorbing solar radiation. Snow cover reflects a huge amount back to space. As air cools over the northern latitudes, it sinks to the surface and the air pressure increases. This results in the huge arctic high pressure areas that frequently develop over Canada. There are other elements that influence the amount of solar heating distribution, but these are the major ones. High pressure and low pressure areas form due to these factors and the battle zones that form between the air masses (the fronts) create the low pressure areas. The pressure gradient or the difference in pressure over a certain distance, determines the strength of the wind. As warm air rises in the developing frontal system (or extra-tropical storm), air pressure drops. Then, surrounding air moves in at the surface to replace the air that has risen. This is called "wind". This flow of air is deflected to the right by the Coriolis Effect. This is a very simplified way of explaining a very complex and technical process that goes on to create a storm system. Now, tropical storms and hurricanes produce wind by lowering air pressures in the center of the low pressure area. The pressure gradient is more extreme in these storms since the difference in pressure is greater over a very short distance (between the center or eye of the storm to the outer edge of the storm's circulation). There are localized wind systems, such as "sea breezes". (Please see the weather fact I added explaining sea breezes in detail).

Dave