May 27 - Beaufort Scale Day

Posted on May 27, 2020

Do you know what empirical means?

It refers to experience - information received through the senses of sight, sound, taste, feeling, and smell.

The Beaufort Scale is an empirical measure of wind speed. Rather than directly measuring the speed of a wind with an anemometer, which has cups that capture the horizontal movement of air particles, the Beaufort Scale relies on conditions on the sea or land that can be observed. 

You may have guessed that the Beaufort Scale was created by a person named "Beaufort." Sir Francis Beaufort, who was born on this date in 1774, served in the Royal Navy as an officer - eventually a Rear Admiral.

Sailors had always kept track of weather, writing about conditions in their logs. However, before Beaufort's Scale, the words used to describe wind speed and therefore force was pretty subjective. One observer might record that there was a stiff breeze just as another observer in the same place, at the same time, might call the breeze soft. 

Beaufort created a scale based on the observation of a frigate's canvas sails. It ranged from 0 to 12, that is from "just sufficient to give steerage to that which no canvas sails could withstand."

Beaufort invented the scale in 1805, and in the late 1830s it was adapted by the entire Royal Navy. In the 1850s the scale was adapted for use on land; the numbers of the scale correlated to the number of rotations of the anemometer.

In 1946, the scale was extended by adding numbers 13 through 17 - the larger numbers being used during, say, cyclones / hurricanes / typhoons. 

Nowadays meteorologists measure and record wind speed in kilometers per hour, but the Beaufort scale is still used with weather forecasts used by those in the shipping industry, and severe weather warnings given to the general public often include terms used in the modern Beaufort Scale. 

Here are a few examples of observations used on the modern Beaufort Scale:

On the sea: if the sea is like a mirror - 0 - Calm.

On land: if smoke rises vertically, 0 - Calm.

On the sea: Large wavelets with crests that begin to break, glassy-looking foam - 3 - Gentle breeze.

On land: Leaves and small twigs in constant motion, light flags extended - 3 - Gentle breeze.

On the sea: Sea heaps up and white foam from breaking waves begins to be blown in streaks, spray can be seen - 7 - High wind, near gale.

On land: Whole trees are in motion, it's hard to walk against the wind - 7 - High wind, near gale.

On the sea: Exceptionally high waves, both small and medium-sized boats cannot be seen when behind the eaves, sea is covered with long white patches of foam, it's hard to see - 11 - Violent storm.

On land: Very rarely experienced inland, trees uprooted, widespread damage to structures - 11 - Violent storm.

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