Table 36 \\g 



BEAUFORT WIND SCALE 



In 1806 Admiral Sir F. Beaufort devised a scale for recording wind force at sea based on the effect 

 of the wind on a full-rigged man-of-war of that era. In 1838 this scale was adopted by the British 

 Admiralty and with but minor changes had come into general use among mariners for specifying the 

 state of the wind at sea. The International Meteorological Committee (Utrecht, 1874) adopted the 

 Beaufort scale for international use in weather telegraphy, and it now has become the chief scale for 

 specifying the force of the wind and is used in all parts of the world, both on land and on sea. 



Since the original Beaufort scale described a state of the atmosphere as manifested by the effects 

 of the wind near the surface, there did not exist originally a set of wind speeds corresponding to the 

 various numbers of the scale. A number of efforts were made to obtain appropriate speed equivalents 

 but it was found difficult to reach agreement on this matter because the effect of wind variation with 

 height was neglected.^ The International Meteorological Committee (London, 1921) requested Dr. G. C. 

 Simpson of the British Meteorological Office to investigate the matter and in 1926 Dr. Simpson pro- 

 posed a set of speed equivalents which were to apply to anemometers exposed 6 meters above the 

 ground. 1 This scale was adopted by the Committee in Vienna (1926). However, the British Meteoro- 

 logical Office continued to use a scale proposed by Dr. Simpson in 1906 2 and applicable to an anemom- 

 eter at a height of about 10 meters above the ground, as did the U. S. Weather Bureau. This scale 

 was based on the empirical equation V = 0.836 B 3/2 where V is the wind speed in meters per 

 second and B the Beaufort force. 



In 1946 the International Meteorological Committee meeting in Paris extended the original Beaufort 

 scale to higher values and redefined the speed equivalents to apply to an anemometer at 10 meters 

 above the ground. TJp to force 11 these values are consistent with the values for a height of 6 

 meters adopted ip Vienna (1926) and are identical with those proposed by Dr. Simpson in 1906. 



Table 36 gives the speed equivalents of the Paris (1946) resolution and also the "descriptive terms" 

 and "specifications for use on land" from the Meteorological Observers Handbook (London, 1939). 



Mean wind speeds at 10 m.* Limits of wind speed at 10 to.* 



3 9 4.4 16 10 7- 10 3.4- 5.4 12- 19 8- 12 



4 13 6.7 24 15 11- 16 5.5- 7.9 20- 28 13- 18 



5 18 9.3 34 21 



6 24 12.3 44 28 



7 30 15.5 55 35 



8 37 18.9 68 42 



9 44 22.6 82 50 



10 52 26.4 96 59 



11 60 30.5 110 68 



12 68 34.8 125 78 



13 76 39.2 141 88 



14 85 43.8 158 98 



15 94 48.6 175 109 



16 104 53.5 193 120 



17 114 58.6 211 131 



Description 

 Force of wind t Specifications for use on land t 



Calm _ Calm, smoke rises vertically. 



1 Light air Direction of wind shown by smoke drift, but not by wind vanes. 



2 Light breeze Wind felt on face; leaves rustle; ordinary vane moved by wind. 



3 Gentle breeze Leaves and small twigs in constant motion; wind extends light flag. 



4 Moderate breeze Raises dust and loose paper; small branches are moved. 



5 Fresh breeze Small trees in leaf begin to sway; crested wavelets form on inland waters. 



6 Strong breeze Large branches in motion; whistling heard in telegraph wires; umbrellas 



used with difficulty. 



7 Moderate gale Whole trees in motion; inconvenience felt when walking against wind. 



8 Fresh gale Breaks twigs off trees; generally impedes progress. 



9 Strong gale Slight structural damage occurs (chimney pots and slate removed). 



10 Whole gale Seldom experienced inland; trees uprooted; considerable structural damage 



occurs. 



11 Storm Very rarely experienced, accompanied by widespread damage. 



12 or 



above Hurricane 



* Resolution 9, International Meteorological Committee, Paris, 1946. 



t Meteorological Office, The Meteorological Observers Handbook, London, 1939. 



* Simpson, G. C, The velocity equivalents of the Beaufort scale. Professional Notes No. 44. Air 

 Ministry, Meteorological Office, London, 1926. See also Anemometers and the Beaufort scale of wind 

 force, Meteorol. Mag., vol. 67, pp. 278-83, January 1933. Kuhlbrodt, E., Ann. d. Hydr. & Marit. 

 Meteorol. Zweites Koppen-Heft, pp. 14-23, 1936. 



2 Simpson, G. C, Meteorological Office, Publ. No. 180, London, 1906. 



SMITHSONIAN METEOROLOGICAL TABLES 



