Estimated reading time: 3 minutes
Beaufort Scale: Introduction
Powerful winds accompanying storms and tempests can cause extensive damage to both people and property. The primary factor contributing to this damage is the velocity of the wind. The impact of the wind on obstacles in its path is quantified in terms of air pressure per unit area on its trapezoidal surface. The relationship between wind velocity and air pressure is mathematically expressed by the following equation:
Air pressure = velocity² x constant
When air pressure is measured in pounds per square foot and velocity in miles per hour, the constant is determined to be 0.004. Consequently, if the wind velocity is 10 miles per hour, the air pressure would be 0.4 pounds per square foot. However, if the wind velocity increases tenfold, the pressure escalates a hundredfold. For instance, with a wind speed of 100 miles per hour, the resulting air pressure would be 40 pounds per square foot. Such air pressure is potent enough to cause significant damage to conventional buildings. Hence, in contemporary construction practices, these factors are crucial considerations. Keeping the above in mind it becomes important to measure wind speed
To assess wind velocity, Admiral Sir Francis Beaufort introduced the Beaufort wind speed scale in 1805, originally designed for maritime use. However, due to its widespread popularity, it quickly found application on land as well. Velocity equivalents were incorporated into the scale to represent different velocities. Initially Beaufort Scale represented zero to 12 digits ,but the scale has now been extended to 17, accommodating velocities exceeding 65 knots. This scale is endorsed by the World Meteorological Organization.
Beaufort Scale for Winds
| Beaufort Number | Wind Characteristics | Wind Speed (knots) | Land Effects | Sea Conditions |
|---|---|---|---|---|
| 0 | Calm | 0 – 1 | Calm, smoke rises vertically | Calm, mirror-like sea |
| 1 | Light Air | 1 – 3 | Direction shown by smoke drift | Ripples, no foam |
| 2 | Slight Breeze | 4 – 6 | Wind felt on face, leaves rustle | Small wavelets, no foam |
| 3 | Gentle Breeze | 7 – 10 | Leaves and small twigs in motion | Large wavelets, crests break |
| 4 | Moderate Breeze | 11 – 16 | Dust and loose paper raised, small branches move | Small waves, crests break clear |
| 5 | Fresh Breeze | 17 – 21 | Small trees in leaf begin to sway | Moderate waves, some spray |
| 6 | Strong Breeze | 22 – 27 | Large branches in motion, whistling heard in telegraph wires | Large waves forming, whitecaps |
| 7 | Moderate Gale | 28 – 33 | Whole trees in motion, inconvenience felt walking | Sea heaps up, white foam from breaking waves |
| 8 | Fresh Gale | 34 – 40 | Twigs break off trees, walking is severely impeded | Moderately high waves, foam streaks |
| 9 | Strong Gale | 41 – 47 | Trees uprooted, considerable structural damage occurs | High waves, dense foam patches |
| 10 | Whole Gale | 48 – 55 | Widespread damage, very dangerous to land structures | Very high waves, continuous foam |
| 11 | Storm | 56 – 65 | High risk of injury or death from flying and falling debris | Exceptionally high waves, widespread foam and spray |
| 12 | Hurricane | 65+ | Extreme conditions, widespread devastation | Phenomenal waves, air filled with foam |
