Beaufort Scale (redirected from Calm wind)

Beaufort scale, a scale of wind velocity devised (c.1805) by Admiral Sir Francis Beaufort of the British navy. An adaptation of Beaufort's scale is used by the U.S. National Weather Service; it employs a scale from 0 to 12, representing calm, light air, light breeze, gentle breeze, moderate breeze, fresh breeze, strong breeze, moderate gale, fresh gale, strong gale, whole gale, storm, hurricane. Zero (calm) is a wind velocity of less than 1 mi (1.6 km) per hr, and 12 (hurricane) represents a velocity of more than 74 mi (119 km) per hr.

Beaufort's original scale was later correlated to wind speed in two different ways. The U.S. and British scale is for winds measured at a 36-ft elevation, while the international scale requires only a 20-ft elevation. The Beaufort scale is the oldest method of judging wind force. Separate scales for tornadoes and hurricanes did not come until the 1970s. The Fujita scale for tornadoes was proposed in 1971 by Tetsuya (Ted) Fujita. Soon thereafter, the Saffir-Simpson scale for hurricanes was formulated by Herbert Saffir and Robert Simpson.

Bibliography

See A. Shaw, Beaufort Wind Scale (1995).

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Beaufort scale

Meteorol an international scale of wind velocities ranging for practical purposes from 0 (calm) to 12 (hurricane force). In the US an extension of the scale, from 13 to 17 for winds over 64 knots, is used

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Beaufort Scale 

a conventional scale for the visual estimation of the force (speed) of the wind, expressed in numbers, by its action on surface objects or wave agitation on the surface of the sea. It was devised by the English admiral F. Beaufort in 1806; at first it was used only by Beaufort himself. In 1874 it was accepted by the Permanent Committee of the First Meteorological Congress for general international

Table 1. Wind force at the earth’s surface according to the Beaufort scale (at a standard altitude of 10 m above an open, even surface)
Beaufort no.	Descriptive term tor wind torce	Wind speed (m/sec)	Action of wind
			on land	on the surface of the sea
0	Calm	0–0.2	Calm. Smoke rises vertically.	Smooth, calm.
1	Quiet	0.3–1.5	Direction of wind shown by smoke drift but not by wind vanes.	Ripples, no spray on the crests.
2	Light breeze	1.6–3.3	Wind felt on face, leaves rustle, wind vane moved by wind.	Short waves. The crests do not break and are glassy.
3	Gentle breeze	3.4–5.4	Leaves and small twigs in constant motion, wind extends light flag.	Short, well defined waves. Crests break, form glassy spray; occasionally whitecaps form.
4	Moderate breeze	5.5–7.9	Wind raises dust and paper, moves small b-anches.	Long waves, whitecaps are frequent.
5	Fresh breeze	8.0–10.7	Small trees sway, small waves crest on water.	Long, but not very large waves, whitecaps are everywhere (spray sometimes forms).
6	Strong breeze	10.8–13.8	Large branches in constant motion, wires on telephone poles hurr.	Large waves form. Large number of foamy crests (spray is likely).
7	Moderate gale	13.9–17.1	Large trees sway, walking against wind difficult.	Waves become large, crests break, foam forms in band on the windward side.
8	Fresh gale	17.2–20.7	Twigs break off trees, walking against the wind very difficult.	Moderately high, long waves. Spray is blown from the crests. Bands of foam lie in strips in the direction of the wind.
9	Strong gale	20.8–24.4	Minor damage; the wind blows off chimneys and tile.	High waves. Foam lies on the windward side in wide, solid bands. Wave crests begin to break and form spray which decreases visibility.
10	Whole gale	24.5–28.4	Considerable damage to buildings, trees are uprooted. Rare on dry land.	Very high waves with long crests which are bent down. Foam is blown by the wind in large clumps of thick, white stripes. The surface of the sea is white with foam. The noise of the waves sounds like blows. Visibility is poor.
11	Storm	28.5–32.6	Widespread damage. Seldom observed on dry land.	Extremely high waves. Small and medium size vessels disappear from view from time to time. The sea is covered by long, white flecks of foam, collecting on the windward side. The edges of waves are covered with foam. Visibility is poor.
12	Hurricane	32.7 and higher	Widespread damage. Seldom observed on dry land.	The air is filled with foam and spray. The sea is covered with bands of foam. Very poor visibility.

synoptic usage. In subsequent years the Beaufort scale was changed and improved. In 1963, the International Meteorological Organization accepted the Beaufort scale given in Table 1 for general practice. The Beaufort scale is widely used in navigation.

K. P. VASIL’EV