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Breaking it Down with Brittney - What Causes Wind

Wind Explainer
Posted at 6:35 AM, Jan 31, 2022
and last updated 2022-01-31 07:35:51-05

Wind is simply air in motion. Usually in meteorology, when we are talking about the wind it is the horizontal speed and direction we are concerned about. For example, if you hear a report of a west wind at 15 mph that means the horizontal winds will be coming FROM the west at that speed.

High and low pressure indicated by lines of equal pressure are called isobars.

Although we cannot actually see the air moving we can measure its motion by the force that it applies on objects. We use a wind vane to indicate the wind's direction and an anemometer to measure the wind's speed. But even without those instruments we can determine the direction.

You have probably seen weather maps marked with H's and L's which indicate high- and low-pressure centers. Usually surrounding these "highs" and "lows" are lines called isobars. "Iso" means "equal" and a "bar" is a unit of pressure so an isobar means "equal pressure". So everywhere along each line is the pressure has the same value.

Pressure gradient force extends from high pressure to low pressure. Which is the wind.

The closer the isobars are drawn together the quicker the air pressure changes. This change in air pressure is called the "pressure gradient". Pressure gradient is just the difference in pressure between high- and low-pressure areas.

The speed of the wind is directly proportional to the pressure gradient meaning that as the change in pressure increases (i.e. pressure gradient increases) the speed of the wind also increases at that location.

Also, notice that the wind direction (yellow arrows) is clockwise around the high-pressure system and counter-clockwise around the low-pressure system. In addition, the direction of the wind is across the isobars slightly, away from the center of the high-pressure system and toward the center of the low-pressure system.