What Causes Wind? And How is Wind Measured?

Fluid dynamics, Turbulence, fluid-solid interfaces, compressibilityˇ­ it always seemed to go against my engineering intuition. for meteorologists around the world the flow of air (which is a fluid) is a consuming passion.

It was the ancient Greek philosopher, Anaximander, who first suggested that there was a scientific explanation for wind. Many of his peers were content with the belief that wind was a result of the breath of gods. This article will explore the scientific explanation, explain wind measurements, discuss colorful United States wind names, and hopefully challenge your wind knowledge! What is Wind?

In very simple terms, wind is the result of air movement over the Earth. Air moves as a result of pressure systems (those ˇ°Hˇ±s and ˇ°Lˇ±s on the weather news maps): from areas of high pressure to areas of low pressure.

There are two reasons that the atmospheric pressures vary around the Earth:

1) The Earth rotates. As it rotates, it drags the atmosphere around with it causing the air to mix with the higher level atmosphere resulting in turbulence and pressure systems.

2) The sun heats. The heating of air around the Earth varies by latitude and time of day. At the equator, for instance, large amounts of sun warm the air causing it to rise. Conversely, the more acute angles of sunlight over the polar regions spread the rays over a greater area resulting in less warming of the air. The resulting effect is that the air over the poles is more dense than the air over the equator.

Local variations also account for pressure variances. Close to the sea or ocean, for instance, on and off-shore air flows will warm or cool quickly as a result of the warmer or cooler land mass.

As air rises, low pressure areas are created below. Air then rushes from the areas of high pressure to fill in the gap. The larger the differences between the pressures, the greater the flow of air between the two points. These differences in air pressure, which cause wind formation, can be easily quantifiedˇ­ and the wind records will amaze you!

How is Wind Measured?

Winds are primarily measured two ways: direction and speed.

Direction is measured using your everyday, wind vane. Whether it's a flag blowing in the wind, a fanciful steeple-sitting rooster, sailboat vane, or a sock, the main purpose of the instrument is to resist the flow of air. This motion causes the instrument to point in the direction of wind movement. Alternatives include watching clouds drift, licking your finger, determining which way smoke is blowing, letting a balloon fly awayˇ­ you get the idea.

Wind speed is measured with an anemometer. Invented in 1667 by a British physicist named Robert Hooke, the classic model possesses three or four cups used to catch wind. By attaching these cups to a rotating calibrated shaft, wind speed can be easily measured. Today's scientific methods include more sophisticated technologies including radar and lasers.

Units of measurement for wind speed vary. The local news shows speak a language we can all related to: ˇ°tomorrow's winds will be in the 17-20 miles per hour range.ˇ± Professions dealing with navigation, such as the National Weather Service, the Federal Aviation Administration and the Maritime Divisions deal in knots. And scientists, trying to standardize to SI units deal in meters (or kilometers or centimeters) per hour (or second).

......