#earthscience #meteorology #physics 

The Beaufort wind force scale (шкала Бофорта) is an empirical measure that relates [[wind speed]] to observed conditions at sea or on land.

The scale was devised in 1805 by Francis Beaufort, a hydrographer and a [[Royal Navy]] officer.

## Scale
| Beaufort number | Description     | Wind speed                     |
| --------------- | --------------- | ------------------------------ |
| 0               | Calm            | < 1 mph<br>0-0.2 m/s           |
| 1               | Light air       | 1-3 mph<br>0.3-1.5 m/s         |
| 2               | Light breeze    | 4-7 mph<br>1.6 - 3.3 m/s       |
| 3               | Gentle breeze   | 8-12 mph<br>3.4-5.4 m/s        |
| 4               | Moderate breeze | 13-18 mph<br>5.5-7.9 m/s       |
| 5               | Fresh breeze    | 19-24 mph<br>8-10.7 m/s        |
| 6               | Strong breeze   | 25-31 mph<br>10.8-13.8 m/s     |
| 7               | High wind       | 32-38 mph<br>13.9-17.1 m/s     |
| 8               | Gale            | 39-46 mph<br>17.2-20.7 m/s     |
| 9               | Strong gale     | 47-54 mph<br>20.8-24.4 m/s     |
| 10              | Storm           | 55-63 mph<br>24.5-28.4 m/s     |
| 11              | Violent storm   | 64-72 mph<br>28.5-32.6 m/s     |
| 12              | Hurricane-force | >= 73 mph<br>>= 32.7 m/s       |
| 13              | -               | 83-92 mph<br>36.9 - 41.1 m/s   |
| 14              | -               | 93-103 mph<br>41.2 - 45.8 m/s  |
| 15              | -               | 104-114 mph<br>45.9 - 50.8 m/s |
| 16              | -               | 115-125 mph<br>50.9 - 55.6 m/s |
| 17              | -               | > 125 mph<br>> 55.6 m/s        |
Numbers 13-17 are only used in Taiwan and mainland China
## Calculation
While the scale is purely empirical, there exists a formula for calculating average wind speeds by scale:
$\LARGE v=1.87B^{1.5}$ mph = $\LARGE 0.836B^{1.5}$ m/s, where B is the Beaufort scale number.