Measuring the Speed of the Wind

2011-10-15 17:50:08.000 – Roger Pushor,  Weather Observer/IT Specialist

Number 2 Heated

Anemometer – Any instrument for measuring and indicating the force or speed of the wind. From the Greek word anemos meaning wind. It is believed that an Italian artist and architect Leon Battista Alberti invented the first mechanical anemometer in 1450.

There are a number of different types of anemometers and they fall into two broad categories, the Velocity anemometers which measure the speed of the wind and the Pressure anemometers which measure the force of the wind. Here at Mount Washington Observatory we have examples of both types and will have one or more anemometers mounted on the tower or deck at any given time depending on the current conditions.

The cup anemometer invented in 1846 by Dr. Thomas Romney Robinson of Armagh Observatory located in Northern Ireland consists of three or four hemispherical cups each mounted on a horizontal arm which in turn are mounted at equal angels to each other on a vertical shaft. Here at the Obs we use this type of anemometer when winds are moderate and there is no icing. This type of anemometer is an example of a velocity anemometer and is found in many weather stations.

Another very common type of anemometer is the windmill anemometer which also measures the velocity of the wind using a propeller on the front and a tail to make it vane into the wind. This type of anemometer is well suited for light to moderate winds when there is no icing.

The sonic anemometer developed in the 1970s uses ultrasonic sound waves to measures the velocity of the wind. The sonic anemometer has the advantage of no moving parts however because of the precise alignment required of the transducers it can be adversely affected by icing.

Probably the most famous anemometer here on the Summit is the one pictured above; this is ‘Number 2 Heated’, the anemometer that measured the 231 mph ‘Big Wind’ on April 12th, 1934. This is a multiple bucket type anemometer and was the most successful anemometer at the Observatory until 1945. This type of anemometer also measures wind velocity. Today Number 2 Heated can be seen on display in the Weather Museum at the summit.

High winds and severe icing at the home of ‘The World’s Worst Weather’ require unique solutions so in 1945 Sgt. Adam J. Eckert of the Observatory Detachment of the Eighth Weather Squadron A.A.F working at the summit experimented with mounting a heated pitot tube on a vane to measure the pressure of the wind as it passed over the summit. This is how the predecessor to our current and very successful Pitot Static Anemometer system was born.

Pitot tubes which are used to reliably measure the speed of an aircraft at high speeds and in severe weather conditions are ideally suited for measuring the winds in all conditions that we find here at the summit of Mount Washington.

In 1945 it was decided that the pitot anemometer would be the primary instrument for wind speed measurements at the observatory and ‘Old Pitot’ was installed. To record the data from the new pitot anemometer system a Hays chart was obtained to record the velocities 24 hours a day. This system ran in tandem with the new pitot anemometer until late 1992. To this day a Hays chart recorder can be found on the ‘Weather Wall’ of the Observatory measuring the pressure of the wind. This pressure can be looked up in a table to determine the speed of the wind.

 

Roger Pushor,  Weather Observer/IT Specialist