Wind speed affects weather forecasting, aircraft and maritime operations, construction projects, growth and metabolism rate of many plant species, and countless other implications. Wind has both speed and direction. Anemometers measure wind speed and wind vanes (weather vanes) measure wind direction. Wind speed, or wind flow velocity, is a fundamental atmospheric quantity. Wind speed is caused by air moving from high pressure to low pressure, usually due to changes in temperature. Note that wind direction is usually almost parallel to isobars [the wavy lines shown on the weather forecasters map indicating high and low pressure!) and not perpendicular as one might expect, due to the rotation of the earth.
ON THE LAND – bring out the kite or batten down the hatches!
Wind is the flow of gases, here on Earth it refers to the movement of air. It is caused by differences in air pressure. Air rushes from high pressure areas to lower ones. Short bursts of wind moving at high speeds are known as gusts. Depending on their strength, winds can be known as a breeze, gale, storm or hurricane.
AT SEA – a sitting duck or catching a wave!
A knot is a unit often used to measure wind speed. Sea breezes occur because heat from the Sun takes longer to warm the sea than the land, creating a difference in air pressure. Sailing ships use wind to power their movement with the help of sails. Sports and recreational activities make use of the wind such as kiteboarding and windsurfing
IN THE AIR – Bernoulli keeping things aloft!
Propellers also can measure wind speed. The propeller blades rotate at a rate proportional to the wind speed. A windsock often is used at airports. A windsock is a cone-shaped bag with an opening at both ends. When it is limp, winds are light; when it is stretched out, winds are strong. Pilots can quickly determine the wind direction and speed along a runway just by observing the shape and direction of a windsock. Another recreational activity which benefits from a sturdy breeze is paragliding.
CAPTURING AN ENERGY SOURCE- watch out Don Quixote…not your average windmill!
Wind can provide energy through the use of wind turbines. Wind energy is the fastest-growing source of electricity production in the world. Of all new generating capacity installed between 2008 and 2012, 36.5% was wind. NextEra Energy (NYSE: NEE), the nation’s largest renewable-energy utility, relies on more than 10,000 net megawatts of wind across 100 farms for 57% of its total capacity. The National Renewable Energy Laboratory estimates that there are 4,150,000 megawatts of wind turbine capacity blowing offshore the United States.
SPACE – it’s windy way out there, too!
Solar wind in outer space is a stream of charged particles that come from the Sun. Saturn and Neptune feature the fastest planetary winds in the Solar System.
MEASURING THE INVISIBLE –
Wind direction is given by the direction from which the wind comes. Depending on the cause of the winds, they can blow in many directions. Some good examples of wind direction are the Easterly winds, which blow from east to west, and Westerly winds which blow from west to east. There are also winds that blow from the north, southwards and also those from the south blowing northwards. There are familiar regional weather terms which indicate notable weather patterns such as “Nor‘easters” which are usually accompanied by very heavy rain or snow, and can cause severe coastal flooding, coastal erosion, hurricane-force winds, or blizzard conditions. In Colorado, “Upslope” conditions develop when there’s a low-pressure center east and south of the Continental Divide. During many upslope storms, the maximum snowfall is recorded at relatively low elevations.
Weather vanes are used to indicate wind direction. A typical wind vane (a.k.a. weather vane ) has a pointer in front and fins in back. The vane includes the common cardinal directions, (N) North, (S) South, (E) East, (W)West. When the wind is blowing, the wind vane points into the wind. For example, in a north wind, the wind vane points northward.
Anemometers are used to measure wind speed. A cup anemometer is a common tool to measure wind speed. The cups catch the wind and produce pressure difference inside and outside the cup. The pressure difference, along with the force of the wind, causes the cups to rotate. Electric switches measure the speed of the rotation, which is proportional to the wind speed. At wind speeds below about 3 mph, the cup anemometer is prone to error because friction keeps the cups from turning. At wind speeds above 100 mph, cup anemometers often blow away or give unreliable measurements. In freezing rain, the anemometer can literally freeze up and stop turning.
Sonic anemometers use sound waves humans cannot hear to measure wind speed and direction. The instrument determines the wind velocity by measuring the time between when the instrument sends a sonic pulse and when it is received.
Wind speed is now commonly measured with an anemometer, but can also be classified using the older Beaufort scale which is based on people’s observation of specifically defined wind effects. At typical home sites, winds might run up to the 70 mph to 100 mph range a few times a year. More normal instantaneous wind speeds top out in the 40 mph to 50 mph range. But for wind energy production, the important range of instantaneous speed is between 10 mph and 25 mph.
