The Why of Wind By Steve Roark TN Dept. Agriculture, Forestry Division

We’ve had some pretty blustery weather lately, demonstrating how powerful wind and weather can be.  Maybe you haven’t thought about it since 8th grade science, but it might be interesting to review why we have wind at all.

 

Wind is movement of air molecules, which like other particles in nature, always move from high concentrations to lower concentrations, seeking equilibrium.  The Sun warms the atmosphere, unevenly. Some parts of the Earth like the equator receive more direct sun rays and are always warm.  The further north you move the sun’s rays are more indirect (at an angle) and the atmosphere is cooler.  The warmer air has fewer air molecules in it and so is lighter in weight, and is called a low pressure area or system.  Air in a cooler atmosphere has molecules that huddle closer together, thus making the air more dense (higher pressure), and is called a high pressure system. So basically wind is air molecules moving north and south to try to equalize the air pressure between high and low pressure areas.  This north/south movement is dragged towards the east by the Earth rotating under the atmosphere, and so the prevailing winds in our area are more or less out of the west.  That’s how your average everyday winds come about.

 

What causes wind to get lively and change direction is when those warm and cold air masses move around and bump into each other.  These bumps where the two air masses collide are called fronts.  TV meteorologists are always talking about either cold or warm fronts moving through our area and bringing some changing weather, rain usually, but always with increasing winds that change direction as the front passes.

 

A warm front is a warm air mass moving into an area with a cold air mass, and as they collide the warm air rises over the cooler air in a slow gradual incline.  As the warm air rises and cools, moisture in it condenses to form flat looking stratus clouds that may eventually drop low intensity rain that can be long duration. As the warm front approaches winds are generally out of the east (high pressure to low pressure remember) and as the front passes the wind will shift to coming from the south/southeast.  Wind speeds are higher but usually not enough to cause concern. So think of an approaching warm front as the warm and cold air masses greeting each other with a slow kiss.

 

An approaching cold front on the other hand is more like a punch in the mouth.  Here a cold air mass moves into an area with a warm air mass.  The cold air has a steeper slope in front of it, so when it collides with the warm air mass it pushes the warm air up very fast and clouds develop as tall puffy cumulus and can go to stormy cumulonimbus size in a hurry.  This rapid rise of air causes very unstable conditions that can form violent weather, including  short duration heavy rains, hail, high winds, even tornadoes.

 

Paying attention to the wind was how people predicted the weather before satellites and such.  So if you’re attentive, wind can tell you things as well.

 

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