Ancient Wind Measurement Wind vanes were perhaps the
- Slides: 37
Ancient Wind Measurement • Wind vanes were perhaps the most ancient meteorological instruments. • Mesopotamian and Sumerian documents, dating back nearly 4, 000 years, describe primitive wind vanes, and streamers were used for wind direction measurement in China during the second century B. C. E.
101 Wind
Why Wind? • Created by differences in pressure. • Air accelerates from high to low pressure • Wind is simply the movement of air
Ancients had other ideas…
Wind Measurement • The famous Tower of the Winds in Athens, dating back at least to 50 B. C. E. , was topped by a wind vane in the form of a Triton • Wind vanes and wind banners were common during the Middle Ages, and were found on many churches, ships, and towers.
Wind direction can be measured with wind vanes
More modern version
Wind speed is measured using anemometers
Development of anemometers
Modern Three-Cup Anemometer
Combo
Sometimes anemometers and wind vanes have had icing issues.
New Sonic Anemometer Old The solution….
Sonic Anemometer
Wind Terminology • Wind direction is the direction from which the wind is coming – Easterly wind from the east – Westerly wind from the west • Given in cardinal directions. . or. .
Wind Direction (degrees) Professionally—generally degrees used
Speed • Generally given in knots – 1 knot = 1 nautical mile per hour= 1. 15 mph – 1 knot is ~. 5 meter per second
Proper Exposure of Wind Instruments • Open area • Sensors at 10 m (roughly 30 ft) above the ground • Not above pitched roof.
Sustained Winds and Wind Gusts • Sustained: usually average of 1 -2 minutes • Gusts: typically strongest 3 -5 second average wind reported during a period. • Typically about a 1. 3 -1. 4 ratio for (gust/sustained), but can be much more in some occasions.
You Can Often See Gusts Over Water—called “cat’s paws”
Why Gusts?
Winds are often far stronger over water than land • Water is much smoother aerodynamically than land • Trees, building, hills, etc. all slow down winds near the surface. • Wind over water can be 50 -100% stronger (or more) than over land.
Estimating Wind Subjectively • Wind direction: flags, low clouds, trees and branches, throw grass in air • Wind speed: Beaufort Scale
Sir Francis Beaufort, 1805
Wind Terminology • Gale: 34 -47 knots • Storm: 48 -64 knots • Hurricane: 65+ knots
Strongest Near Surface Winds • Anemometer: 231 mph, Mt. Washington, NH 1934 • Radar: 318 mph, OK City Tornado, 3 May 1999
The NW Wind Record
Columbus Day 1962: At Cape Blanco there were 150 mph with gusts to 179! Strongest winds on bluffs and windward slopes of coastal orography
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