One of the first scales to estimate wind speeds and the effects was created by Britain's Admiral Sir Francis Beaufort (1774-1857). He developed the scale in 1805 to help sailors estimate the winds via visual observations. The scale starts with 0 and goes to a force of 12. The Beaufort scale is still used today to estimate wind strengths.
|Beaufort Force||Description||Effects on land||knots||km/h||mph|
|0||Calm||Smoke rises vertically.||Less than 1||Less than 1||Less than 1|
|1||Light Air||Direction of wind shown by smoke drift, but not by wind vanes.||1 - 3||1 - 5||1 - 3|
|2||Light breeze||Wind felt on face; leaves rustle; ordinary vanes moved by wind.||4 -6||6 - 11||4 -7|
|3||Gentle breeze||Leaves and small twigs in constant motion; wind extends light flag.||7 - 10||12 - 19||8 - 12|
|4||Moderate breeze||Raises dust and loose paper; small branches are moved.||11 - 16||20 - 29||13 - 18|
|5||Fresh breeze||Small trees in leaf begin to sway; crested wavelets form on inland waters.||17 - 21||30 - 39||19 - 24|
|6||Strong breeze||Large branches in motion; whistling heard in telegraph wires; umbrellas used with difficulty.||22 - 27||40 - 50||25 - 31|
|7||Near gale||Whole trees in motion; inconvenience felt when walking against the wind.||28 - 33||51 - 61||32 - 38|
|8||Gale||Breaks twigs off trees; generally impedes progress.||34 - 40||62 - 74||39 - 46|
|9||Strong gale||Slight structural damage occurs (chimney-pots and slates removed).||41 - 47||75 - 87||47 - 54|
|10||Storm||Seldom experienced inland; trees uprooted; considerable structural damage occurs.||48 - 55||88 - 101||55 - 63|
|11||Violent storm||Very rarely experienced; accompanied by wide-spread damage.||56 - 63||102 - 117||64 - 73|
|12||Hurricane||Whole hangars disappear.||>64||>119||>74|
the Griggs-Putman index of deformity provides information on average wind speeds.
Given an obstruction of height H, the air will generally be disturbed in an area roughly bell shaped with a height of up to 2H over an area that starts 2H before the obstruction and continues for 20H after it. On the other hand, a smoothly rolling hill will concentrate the wind at the peak and provide higher velocities at the hilltop.
|file: /Techref/other/wind.htm, 4KB, , updated: 2012/12/7 10:15, local time: 2021/1/23 18:32,
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