Wind is defined as the movement of air, especially a natural horizontal movement. Meteorologist are interested in measuring four properties of wind: (1) the direction in which the wind is blowing; (2) the speed of the wind; (3) wind gust; and (4) any wind shifts that may occur.
Wind direction refers to the direction in which the wind is blowing. Meteorologist usually record wind direction according to its cardinal direction, or compass points—East, West, Southeast, etc . . . The students can take this exercise one step further by stating the degree at which the wind is blowing. For example, they can record the wind direction as 180 degrees South, or 230 degrees Southwest, etc . . .
Wind speed is recorded according to the rate of motion of the air in relationship to a specific unit of time. Therefore wind speed is recorded in knots (nautical miles per hour). Wind speed can also be measured in miles per hour (mph).
Gusts are rapid fluctuations in wind speed with a variation of 10 knots or more between peaks and lulls. If there is a fluctuation in wind speed between 15 knots and 20 knots, sustained for at least one minute, they are called squalls. If the wind speed fluctuates above 20 knots, they are known as peak gust—the highest wind speed that can be recorded.
Wind shifts are changes in wind direction of 45 degrees or more that occur in less that 15 minutes. Wind shifts of that magnitude are normally an indication that a cold front is passing through. Whenever these types of wind shifts occur meteorologist can confidently forecast that a storm is on its way. Atmospherically, there will be a rapid drop in temperature and dew point, and a rise in air pressures.
The two instruments in which meteorologist depend upon to measure the four properties of wind are: (1) wind vane—an instrument which indicates the direction that the wind is blowing; and (2) Anemometer —an instrument which measures wind speed.
A wind vane is simply a large arrow on a pivotal base that points in the direction which the wind is blowing. The wind vane should be placed in an area free from buildings, trees, or any other objects that don’t allow the wind to blow freely. A set of direction (cardinal) indicators should be placed at some point underneath the arrow, which are directly related to the cardinal compass points. Directions for building a wind vane, along with an illustration, can be found in Appendix 2 at the end of the unit.
An anemometer is an instrument which measures the speed of wind. This instrument must be placed high above the ground and away from anything that can obstruct the flow of air. Even though there are several different types of anemometers, the Robinson Anemometer is the most commonly used because it works well under a great number of conditions. The wind speed is determined by the number of turns of the wheel in a certain length of time.