The Beaufort Scale

The Beaufort scale is an empirical measure for describing wind intensity based mainly on observed sea conditions. Its full name is the Beaufort wind force scale.

The scale was created in 1805 by Sir Francis Beaufort, a British naval officer and hydrographer. At that time naval officers made regular weather observations, but there was no scale and so they could be very subjective - one man's "stiff breeze" might be another's "light air". The initial scale from zero to twelve did not reference wind speed numbers, but related qualitative wind conditions to effects on the sails of a man of war, then the main ship of the Royal Navy, from "just sufficient to give steerage" to "that which no canvas [sails] could withstand."

The scale was adapted to non-naval use from the 1850s, with scale numbers corresponding to cup anemometer rotations. In 1906, with the advent of steam power, the descriptions were changed to how the sea, not the sails, behaved and extended to land observations. Rotations to scale numbers were standardised only in 1923.

George Simpson, Director of the UK Meteorological Office, was responsible for this and for the addition of the land based descriptors. The measure was slightly altered some decades later to improve its utility for meteorologists. Wind speed on the Beaufort scale can be expressed by the formula:

v = 0.837 B^3/2 m/s

where 'v' is wind speed and 'B' is Beaufort scale number.