Observing Climate - Surface

Transcription

1 Observing Climate - Surface 3-1 Wind Science Concepts Definition Anemometer Wind Vane Velocity Vectors Speed Direction Energy - Kinetic Energy

2 3-2 Definition How would you define the wind? Wind velocity is the movement or motion of air relative to the Earth s surface Science quotes of 5th and 6th graders - The wind is like the air, only pushier. - Velocity is defined as the change in location with time V = (Change in location) (Change in time) = ( x 2 - x 1 ) ( t 2 - t 1 ) - Vector - direction and magnitude Horizontal wind is usually about 100 times larger than the vertical wind

3 3-3 Measurement Wind Speed - Anemometer - From Greek word for wind, anemos - Deflection anemometer > Invented in 1450 by the Italian architect Leon Battista Alberti Similar to Weather Rocks - vincimus/32anem_e.html This rock is the perfect weather indicator, more accurate than the local weather person. This is how it works. If the rock is swaying it is windy, dry, it is fair, wet it is raining, white, it is snowing, jumping up and down, an earthquake is upon us, under water, there is a flood. If there is a shadow under the rock, it is sunny.

4 3-4 Measurement Wind Speed (Con t) /Robinson-cup-anemometer.html - Cup anemometer - Invented in 1846 by Thomas Romney Robinson > Cups connected to gears that caused gages to turn. Observer reads gages initially and then again five minutes later. The difference between the readings indicates how much wind has passed by the anemometer. Multiplying this by 12 yields the miles of wind per hour. > Today cups connected to the shaft of a DC generator > Too sluggish for accurate measurements of gusts - Hot-wire anemometer - Measures heat loss from a small heated wire. > Much more accurate measurements of wind gusts

5 3-5 Measurement Wind Speed (Con t) - Portable Anemometer > Kestrel 1000 Pocket Anemometer Small rotating fan blades for anemometer anemometers9.html

6 3-6 Measurement (Con t) Wind Direction - Vane > Points direction from which the wind is blowing SUOMI/TUOTTEET/anturit.html Refined version of barn-top vane Combined Wind Instruments - Belfort Model 2000 > Measures wind speed using a stainless steel cup anemometer > Measures wind direction using an aluminum wind vane

7 3-7 Measurement (Con t) Combined Wind Instruments (Con t) - Belfort Aerovane Wind Transmitter - Model 120 > Wind speed is sensed by an impeller mounted to the shaft of a DC generator > Measures wind direction by tail wind vane products/wind/m120.html Location - 10 m above ground, in open space, away from buildings, etc.

8 3-8 Units Wind Speed - Meters / second (m / s) - Miles per hour (mph) Third Grade Joke - What has three feet but can t walk? A yard > Statute mile Measure of distance, equivalent in England and the U.S. to 5,280 ft A Story About Determining a Degree of Arc, i.e., A Nautical Mile This would be a ruler defined by gravitational pull of the earth rather than something arbitrary like the king s foot, and it could provide a standardized measurement for all nations. One wishes that it would be universal, La Condamine wrote, giving voice to a sentiment that, fifty years later, would inspire France to invent the meter. Whitaker, R., 2004: The Mapmaker s Wife - A True Tale of Love, Murder, and Survival in the Amazon. Bantam Dell. ISBN , p. 164.

9 3-9 Units (Con t) Wind Speed (Con t) - Nautical miles per hour or knots (kt) > Nautical mile 1 minute of arc on the Earth on a great circle, i.e., divide the Earth s circumference into 360 ; then divide a degree into 60 min; 1,852 m = 1,076 ft Kilometer = 1 / 10,000 the distance from the North Pole to the Equator on a line through Paris (Defined in 1791 by the French Academy of Sciences) A Story About Determining a Degree of Arc, i.e., A Nautical Mile Poleny s invention was designed to improve on the standard method s for calculating a ship s speed, which involved throwing overboard a weighted wooden disk attached to a rope with knots tied at equal distance along its length. By counting the number of knots that reeled out over a given period of time, sailors could get a rough measure of how fast the ship was moving. The problem was that this method did not account for the speed of the current. Whitaker, R., 2004: The Mapmaker s Wife - A True Tale of Love, Murder, and Survival in the Amazon. Bantam Dell. ISBN , p. 66.

10 3-10 Units (Con t) Wind Direction - Direction from which the wind is blowing - Compass points - N, NE, NNE, etc. - Degrees - North = 0, East = 90, etc. Conversions 1 kt = mph = m / s 1 m / s = kt = mph