Atmosphere And Weather

The Beaufort Wind Scale



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Throughout the ages, mankind have evolved and manipulated their environment to the extent that they have become the most successful animals on the planet. However, the one thing that they have never been able to reckon with is the weather. It is a powerful and invasive force that governs our lives and helps to create the environment that we live in.

Although the hydrographer, Sir Francis Beaufort cannot be credited with inventing the nautical terms for the varying intensity of wind conditions, he can be remembered for his successful attempt to standardize the practice of estimating the level and force of wind speed.

Originally intended for his own use as a kind of shorthand for his notations whilst aboard ship, he initially created a scale of 13 classes and used them in relation to the sails of a man of war vessel which was the main seagoing ship of the Royal Navy at the time.

The scale runs from 0, "just sufficient to give steerage" to that of force 12, "that which no canvas sails could withstand." This would tell the mariner that at zero he will need to put all sails up and at force 6 he will need half his sails and at 12 he will need to stow all his sails and batten down to withstand the worst of weather.

In 1944 the extra categories of 13 17 were added to the scale to take into account of tropical storms such as Typhoons and Hurricanes. In 1960 the Beaufort scale was modified even further by adding 'probable average' and 'maximum expected' wave heights.

The Royal Navy made the Beaufort scale mandatory for vessels in the late 1830s. It became used by non navy personnel from the 1850's with the numbers of the scale being translated for use in conjunction with cup anemometer readings.

With the growth of steam power came the need to further standardize the scale with sea conditions changed for sail conditions and land observation added in 1923 by George Simpson, Director of the UK Meteorological Office.

Although the Beaufort scale has now been largely replaced by the SI-based units m/s or km/h, the severe weather warnings that you still hear on the radio and the television are all still the same type that have been used for the last 100 years.

The modern Beaufort scale Land and Sea:

Force 0. *CALM* (Sea) Under 1 knot The water is mirror like (Land) Under 1 mph smoke rises vertically.

Force 1. *LIGHT AIR* (Sea) 1-3 knots. Water has appearance of tiny scales or ripples there is no foam crest. Wave height 0.25ft. (Land) 1-3mph Direction of wind shown by smoke drift but not by weather vane.

Force 2. *LIGHT BREEZE* (Sea) 4-6 knot. Water shows small waves; crests of glassy appearance, not breaking. Wave height. 0.5-1ft. (Land) 4-7mph. Wind felt on face. Leaves gently moved. Weather vanes register.

Force 3. *GENTLE BREEZE* (Sea) 7-10 knots Large wavelets; crests begin to break; scattered whitecaps. Wave height 2-3ft. (Land) 8-12 mph. Leaves and small twigs are constantly moved around and wind extends a small flag.

Force 4. *MODERATE BREEZE* (Sea) 11-16 knots Small waves, becoming longer; numerous whitecaps. Wave height 3.5-5ft (Land) 13-18mph. Whirls dust and small paper, branches sway.

Force 5. *FRESH BREEZE (Sea) 17-21knots. Medium waves taking a longer form; lots of whitecaps; some spray. height 6-8ft (Land) 19-24mph Small trees sway and crested wavelets begin to form on inland water.

Force 6. *STRONG BREEZE* (Sea) 22-27knots. Larger waves form; whitecaps everywhere; more spray. Wave height 9.5-13ft (Land) 25-31mph Large branches moving and whistling heard in telegraph poles and under eaves. Umbrellas blow inside out.

Force 7. *NEAR GALE* (Sea) 28-33knots Sea heaves up; white foam from breaking waves begins to be blown in streaks. Wave height 13.5-19ft (Land) 32-38mph. Whole trees in motion and difficulty walking against the wind.

Force 8. *GALE* (Sea) 34-40knots. Moderately high waves of greater length; edges of crests begin to break into spindrift; foam is blown in well-marked streaks. Wave height 18-25ft. (Land) 39-60mph. Breaks twigs off trees and generally impedes progress.

Force 9. *STRONG GALE* (Sea) 41-47knots waves; sea begins to roll; dense streaks of foam; spray may begin to reduce visibility. Wave height 23-32ft. (Land) 47-54mph. Slight structural damage occurs. Dislodges chimney pots and slates.

FORCE 10 *STORM* (Sea) 48-55knots. High waves with overhanging crests; sea takes white appearance as foam is blown in very dense streaks; rolling is heavy and visibility is reduced. Wave height 29-41ft. (Land) 55-63mph. Seldom experienced inland. Trees are uprooted and considerable structural damage occurs.

Force 11. *VIOLENT STORM* (Sea) 56-63knots. Exceptionally high waves; sea covered with white foam patches; visibility further reduced. Wave height 37-52ft. (Land) 64-72mph. Very rarely experienced accompanied by widespread damage.

Force 12. *HURRICANE* (Sea) 64knots and over Air filled with foam; sea completely white with driving spray; visibility greatly reduced. Wave height 45ft and over. (Land) 73mph and over, resulting in devastation to life and property.

After being shipwrecked at the age of fifteen, and in danger of starvation, because of a badly drawn up sea chart, Beaufort became intent on relaying the message of the positive aspects of education and the review and development of accurate charts for those risking their lives on the high seas.

Thanks to the efforts and the exacting nature of his work, he leaves a legacy of illuminating correspondence. Although his scale has been much modified over the last hundred years, he would probably have approved a great deal of the metamorphosis of his original work.




http://www.metlink.org/data/beaufort.php
http://www.fatbadgers.co.uk/Britain/beaufort.htm
http://www.metoffice.gov.uk/education/secondary/students/beaufort.html
http://en.wikipedia.org/wiki/Beaufort_scale

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