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The fastest wind speed not related to tornadoes ever recorded was during the passage of Tropical Cyclone Olivia on 10 April 1996: an automatic weather station on Barrow Island, Australia, registered a maximum wind gust of 113.3 m/s (408 km/h; 253 mph; 220.2 kn; 372 ft/s) [6] [7] The wind gust was evaluated by the WMO Evaluation Panel, who found ...
Direction shown by smoke drift but not by wind vanes 2 Light breeze 4–6 knots 4–7 mph 6–11 km/h 1.6–3.3 m/s 1–2 ft 0.3–0.6 m Small wavelets still short but more pronounced; crests have a glassy appearance but do not break Wind felt on face; leaves rustle; wind vane moved by wind 3 Gentle breeze 7–10 knots 8–12 mph 12–19 km/h
This provides a method to calculate the roughness length by measuring the friction velocity and the mean wind velocity (at known elevation) in a given, relatively flat location (under neutral conditions) using an anemometer. [4] Of note is that, in this simplified form, the log wind profile is identical in form to the dimensional law of the wall.
In common usage, wind gradient, more specifically wind speed gradient [1] or wind velocity gradient, [2] or alternatively shear wind, [3] is the vertical component of the gradient of the mean horizontal wind speed in the lower atmosphere. [4] It is the rate of increase of wind strength with unit increase in height above ground level.
Wind speed is measured by anemometers, most commonly using rotating cups or propellers. When a high measurement frequency is needed (such as in research applications), wind can be measured by the propagation speed of ultrasound signals or by the effect of ventilation on the resistance of a heated wire. [11]
The time that a sonic pulse takes to travel from one transducer to its pair is inversely proportionate to the speed of sound in air plus the wind velocity in the same direction: = (+) where is the time of flight, is the distance between transducers, is the speed of sound in air and is the wind velocity. In other words, the faster the wind is ...
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The equation to estimate the mean wind speed at height (meters) above the ground is: = [ + (,,)] where is the friction velocity (m s −1), is the Von Kármán constant (~0.41), is the zero plane displacement (in metres), is the surface roughness (in meters), and is a stability term where is the Obukhov length from Monin-Obukhov similarity theory.