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Estimating wind speed

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.

Area of disturbed wind around obstructions

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.


See also:

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