How does an Anemometer Work?

What is an Anemometer?

An anemometer is a common weather instrument used to measure the speed of the wind. There are several types of anemometers, ranging in complexity; the most basic models measure the wind speed, or more complex ones can measure wind speed, wind direction and wind pressure.

How do the Different Anemometers Work?

The spinning cup anemometer measures wind speed only. It is the most common type of anemometer and is also the most basic model. The cup anemometer consists of three or four cups (one with a magnet attached to it) positioned on a 45 degree angle and mounted to a vertical pole. As the wind blows, it catches in the hollow of one or more of the cups, and forces the anemometer to spin on the pole. Each time the anemometer completes a full rotation, the magnet on the cup is detected by a reed switch, triggering an output pulse proportionate to the wind speed. The number of pulses is counted over a period of time, and converted into an average wind speed that is recorded on a display or weather station.

The spinning cup anemometer.

A slightly more complex type of anemometer is the sonic anemometer. The sonic anemometer uses ultrasonic sound waves to measure the wind speed, as well as the direction. Two pairs of ultrasound transducers (devices that both emit and receive sound waves), are positioned approximately 4 to 8 inches apart, facing one another. In turn, each transducer emits an ultrasonic sound wave into the wind, towards the opposite transducer. If the wind is behind the sound wave, it will cross the gap faster, or if the wind is in front of the sound wave, it will cross the gap more slowly. By calculating the time it takes for the sound wave to cross back and forward across the gap we can tell the speed of the wind - a weather station makes this calculation for us and displays it as wind speed. The wind direction is also determined by examining which angle the wind passed through the ultrasonic waves. Sonic anemometers are popular because they can take very accurate readings and require no moving parts.

The sonic anemometer.

Another basic anemometer is the windmill anemometer. The windmill anemometer consists of shaft with a tail fin and a propeller positioned on opposite ends and mounted to a vertical pole. Wind blowing against the tail end causes the anemometer to rotate until it faces into the wind (indicating wind direction), which in turn causes the blades of the propeller to rotate. The wind speed is calculated using a magnet and reed switch just like on the spinning cup anemometer.

Anemometers and Weather Stations

Most weather stations have anemometers that will measure the wind speed and direction, as these two components are generally recognised as the common factors for determining the wind.

Some examples of good weather stations that measure these are the La Crosse WS-2315 or the Wireless Davis Vantage Pro2 .

How does the Wind affect us?

The biggest thing we will often notice about the wind is the ‘wind chill factor’, which determines how cold we feel when we are outside. The wind chill temperature is always equal to or below the air temperature.

Our bodies maintain our internal temperature at around 98.6°F and we are most comfortable when the air temperature is between 60 and 80°F. In these temperatures, our skin temperature is around 90°F because the excess heat from our bodies leaves to help cool our skin. If wind is blowing past our skin, more heat escapes into the environment reducing the skin temperature further and we feel colder.

Anemometers are a great tool for measuring the weather. They are also a handy learning tool for teaching kids about the weather – and they help you know what days to wear a jersey! Check out our Weather Station Store to find more great tools to help you forecast and monitor your neighbourhood weather.