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Wednesday, October 29, 2014 - 1:34pm

What "Weather Instruments" Measure Wind?

Weather Talk

POSTED: Thursday, January 30, 2014 - 2:27pm

UPDATED: Thursday, January 30, 2014 - 2:35pm

A Variety of Devices are Used to Determine Wind Direction and Speed at All Levels of our Atmosphere

We here in the Borderland are almost to the time of year when we will have to be thinking about our “windy season”. We will have to do a once over through the front and back yard to see if there are things that may become airborne or blown over. We have to find a good spot to shelter our trash cans and our pets. Small dogs, cats and people for that matter have trouble keeping upright and stable in our powerful Borderland gusts! In today’s “Weather Talk” I thought I would talk about “Wind Instruments”. No I am not talking about a clarinet, flute, bassoon or saxophone! (Even though my nephew, Mason Owens can sure play a mean sax! He is one of the best in Colorado!) I digress. I am talking about the tools, instruments we use to measure wind speed and direction at the surface and way above our heads. I will describe surface equipment, mid level weather balloons and upper level wind analysis instruments.

A very, old yet reliable weather instrument for figuring out wind direction is a weather vane. When we hear weather vane images a rooster on top of a barn or house with a swiveling arrow with directional markers beneath the arrow, aligned with the geographic directions. The tail has more surface area and is blown away from the direction the wind is blowing and the arrow is blown towards. A northeast wind, the arrow would be facing towards the northeast, the direction from the wind is blowing.

Another device used to measure the wind is a wind sock. This instrument is found mainly at airports, seaports and other open areas such as mountain roads where a very visual indication of the wind is needed. The are also used on outdoor stadium goal posts to help the kicker on the team make adjustments for his kick depending on wind speed and direction. Wind socks do actually show both the direction and speed of the wind. The direction is shown when the wind blows into the open end and the sock points the way the wind is blowing. An indication of wind strength is given by the shape and movement of the wind sock. If it is flapping about gently the wind is only light, whereas if it sticks out in a straight line the wind is much stronger.

The instrument we use to measure wind speed is called an anemometer.
Most anemometers today are cup anemometers and consist of three or more hemispherical cups mounted on a vertical shaft; the rate at which they rotate is directly proportional to the speed of the wind. The spinning of the cups is usually translated into wind speed through a system of gears or electronically measure the speed by calculating how fast the cups rotate.

The Aerovane is another common instrument used to measure both wind speed and direction. I have always thought that it looks like an airplane with no wings. It consists of a three bladed propeller that rotates a rate proportional to the wind speed. The vane has a streamlined shape and a vertical fin that the blades facing the wind. This is attached to a computer which continuously displays and records both wind speed and direction.

The simplest way to determine the wind speed above the surface is with a pilot balloon. These balloons are usually launched twice a day by the area National Weather Service office and as needed by the military. A pilot balloon is a small balloon filled with gas, usually helium or hydrogen, that is released from the surface. A device is actually an important piece of weather equipment called a radiosonde. A radiosonde is a battery-powered instrument that is suspended below the weather balloon. This device measures the vertical profile of wind, temperature, pressure and humidity as the balloon rises to about 20 miles above the ground. While in flight, radiosonde sensors obtain data for wind direction and speed. Radiosonde data is then transmitted and received by a ground-tracking receiver, which processes it for transmission to weather forecasters and other data users. The data is sent out every 30 seconds to every minute. This information is a primary source of upper-air data for weather prediction models. The observation of winds using a radiosonde balloon is called a rawinsonde observation.

At altitudes higher than 20 miles rockets and radar can tell us about wind flow. One type of rocket ejects an instrument attached to a parachute that drifts with the wind as it slowly falls towards the earth. While it is descending a radar on the ground tracks the unit and determines the wind information from that level of the atmosphere. There are other rockets that eject metal strips at a desired level. Again, a radar tracks the drifting pieces of metal, which provide valuable wind speed and direction data at high altitudes.

There is yet another device, similar to radar called a lidar. Lidar is short for Light, Detection And Ranging. This device uses infrared or visible light in the form of a laser beam to determine wind information. Basically it sends out a narrow beam of light that is reflected from particles, such as dust, pollution or smoke. It measures the wind velocity by measuring the movement of these particles.

Sometimes in remote locations of the world, satellites are used to obtain wind speed. Geostationary satellites work the best. These are satellites positioned over a certain location. The satellites show the movement of clouds. The direction of cloud movement indicates wind direction and the horizontal distance the cloud moves during a given time indicates the wind speed.

Even though the wind can be annoying and a hindrance for our outdoor projects and activities it is very important we use all these “wind instruments” to measure its direction and speed. From anemometers and areovanes measuring the velocity and direction of the wind at the surface, to pilot balloons sending us wind data as they ascend, to lasers, radars and satellites measuring the high altitude winds, they are all valuable in weather forecasting. Now, if you want to talk about the other “wind instruments” I would be more than happy to! I played trombone for 15 years and I am a big music fan. I am also going to be the agent for my nephew, Mason Owens, the sax player; I will let you know when his next project drops!

Chuck DeBroder, Chief Meteorologist
KTSM, NewsChannel 9, NBC, El Paso, TX
cdebroder@ktsm.com
www.facebook.com/pages/Charles-DeBroder/
www.twitter.com/ Chuck DeBroder NC9 @wxchuckNC9
 

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