Measuring wind speed is a fundamental part of meteorology as it often informs predictions for other weather patterns, such as storms. Wind speed is caused by air moving from high pressure to low pressure, which, in turn, is caused by changes in temperature.
Wind speed measurements are essential for aviation and maritime operations, weather forecasting, construction, plant growth and seed dispersal, and many other industries and biological functions.
So, how exactly do we go about measuring the wind? And what tools do we use to do it?
Find out with us as we explore the tools used to measure wind speed.
Wind speeds and wind pressures are measured using an anemometer. There are many types of anemometers, and some of the most useful ones still operate using the same basic technology used when they were first created.
The word anemometer comes from the Greek 'anemos,' meaning wind, and 'metron,' measure. They are distinct from wind vanes, which measure wind direction rather than the speed of the wind itself.
So let's jump in and find out when the anemometer was invented and who invented it.
Italian architect and author Leon Battista Alberti is thought to have invented the anemometer. He wrote about his invention for measuring wind speed in the first known reference to an anemometer in 1450.
Much of the basic technology behind the anemometer has not changed much since it was first invented. Though there have been some advancements and developments in modern anemometers, many still use the technology developed by Alberti all those centuries ago.
Anemometers are used in the majority of weather stations worldwide. Wind speed indicates a shift in weather patterns. It is used for predicting storms and other weather types that can inform and warn the people local to the area, as well as people in certain professions such as pilots or ship captains.
Engineers and physicists also sometimes use laser anemometers in velocity experiments. Laser anemometers calculate the wind speed around vehicles and are used to help improve aerodynamics.
The World Meteorological Organisation and the International Civil Aviation Organisation use meters per second (m/s) to measure and report wind speed.
However, other measurements such as miles per hour, kilometers per hour, knots, or feet per second are still also used in some countries and by specific industries and sectors.
Several factors affect wind speed, including the pressure gradient, Rossby waves, jet streams, and other weather patterns.
- The pressure gradient is the term used to describe the pressure difference between two atmospheric points or two points on the Earth's surface. The more significant the difference in pressure, the faster the wind speed.
- Rossby waves are atmospheric undulations that move from West to East across hundreds of miles. Rossby waves are contained within larger jet streams that move across the world.
- Local weather conditions influence wind speed as larger atmospheric factors create the wind and are then influenced by the local climate it comes into contact with.
There are many different types of anemometers. Some count the number of revolutions made by blades that are pushed by the wind over a certain period. Others use heated wires to judge the time it takes for their temperature to drop. Other anemometers use changes in air pressure to gauge the wind speed or laser beams to calculate the speed of particulates in the air carried by the wind, and some even use the speed of sound waves.
So let's take a closer look at the details of some of these contraptions.
The cup anemometer is the most commonly used, and the three-cup anemometer is currently the industry standard for wind resource assessment. The basic design is three or four cups attached to horizontal arms placed around a vertical rod. When the wind blows, it catches in the cups and causes the rod to spin. The stronger the wind, the faster the rod spins.
The device counts the number and frequency of the rotations. Because the wind speed is inconsistent, the readings are averaged over a period of time to judge the wind speed. This means that the actual wind speed will vary, but the measurement is consistent.
Vane anemometers are similar to cup anemometers, though the axis is horizontal rather than vertical. As the name suggests, a vane anemometer also uses a wind vane, propeller, or similar, to catch the wind as it blows. In this way, it is similar to an upright fan.
As with cup anemometers, the fan's speed is measured by a rev counter that calculates and converts the reading into a wind speed.
The vertical standing and use of a wind vane or propeller give vane anemometers the appearance of a windmill; thus, they are sometimes known as windmill anemometers.
Hot wire anemometers
Hot wire anemometers employ a very fine wire that is heated to a few degrees above the current temperature. The air that flows past the wire then cools it. A wind speed reading can then be taken based on the relationship between the temperature of the metal and the time it takes to cool.
Hot wire anemometers are very delicate and have a high-frequency response, which makes them ideal for the study of turbulent flows.
Laser Doppler anemometers
Laser Doppler anemometers use a laser to measure the flow of particulates that cross through the beam. A detector then measures the speed of the particulate movement to calculate the wind speed around the anemometer.
Ultrasonic anemometers use ultrasonic sound waves to measure wind speed. They send sonic pulses between pairs of transducers and measure the time the flight takes. The longer it takes, the stronger the wind.
Ultrasonic anemometers can also be used as thermometers as the speed of sound varies with temperature as well as wind speed.
There are also acoustic resonance anemometers - another type of sonic anemometer - which are similar to ultrasonic anemometers but are a more modern variant.
Ping-pong ball anemometers
Ping-pong ball anemometers are a DIY version that school children often make.
Simply tie a ping-pong ball to a bit of string attached to a vertical apparatus. Then, when the wind blows, it lifts the light-weight ping-pong ball, and you can measure the angle between the ball and the vertical apparatus, which can provide a very rough approximation of the wind speed.
Plate anemometers were the first type of anemometer invented by Alberti around 1450. It uses a flat plate suspended from the top of a device deflected by the wind. The pressure of the wind against the plate is balanced by a spring, and the compression of the spring provides a gauge of the wind speed.
Plate anemometers are relatively unresponsive compared to other anemometers. Therefore, they are not good at reading speeds of light winds and are generally quite inaccurate. However, they are still occasionally used to trigger high wind alarms.
Tube anemometers were first developed in the late 18th century and originally consisted of a glass tube that contained a liquid. One end of the tube was bent to face the wind flow, while the other was capped. When the wind blows into one end and not the other, it creates an imbalance in pressure which causes the liquid to rise on one side but not on the other. The elevation difference between the two is then used to calculate the wind speed.
Tube anemometers can be exposed to the wind for many years and require no maintenance or attention. This gives them a strong advantage over other types of anemometers that often require regular oiling, repairs, or replacements, as they are exposed to the elements.
Though durable and relatively accurate in high winds, tube anemometers are less effective in low winds.
Pitot tube static anemometers use the same principle as a regular tube anemometer but have a slightly different design. The pitot tube has two ports: pitot (used for measuring pressure) and static (a sealed end used as the control).
The fastest wind speed ever recorded that was not related to a tornado was on April 10, 1996, in Barrow Island, Australia. The weather station measured a wind gust of 113.3 m/s (408 km/h, 253 mph, 220.2 knots, 372 ft/s). The anemometer that took the reading was mechanically sound and was installed 10 meters above ground level.
Wind speeds during tornadoes would exceed this reading. However, it is both difficult and dangerous to measure wind speeds in such an event, and the wind would likely destroy the equipment.
One method used to estimate wind speed during extreme weather phenomena is to use Doppler on Wheels - a remote anemometer that can approximate wind speeds from afar.
Using this method, one reading during a tornado in Oklahoma in 1999 measured a wind speed of 135 m/s (490 km/h, 300 mph, 262 knots, 440 ft/s). This would represent the fastest-ever recorded wind speed on land. However, wind speeds recorded by Doppler on Wheels are not considered official records due to their inaccuracy.
Anemometers are used for measuring wind speed, and some can also be used for measuring wind pressure and temperature. They are important tools for meteorologists and physicists, and the measurement of wind speed is vital for many industries. There are many different types of anemometers, and each has its benefits and drawbacks.
Though it may seem esoteric and unimportant, if it weren't for our ability to measure wind speed, we would not be able to fly planes, ship cargo, predict the weather, plan for harvests, and many other fundamental activities. So, next time you know what to wear for tomorrow's rain, get a package shipped from abroad, or take a flight to a foreign country, be thankful to Leon Battista Alberti and the anemometer for making it all possible!