Definition of Beaufort wind scale
Beaufort wind scale definition - medical term A widely used wind force scale whih is a simple numerical
relationship to wind speed based on an observation of the effects of the wind. The
Beaufort wind scale is of importance in preparations for a tropical storm or hurricane.
The scale is named for Rear-Admiral, Sir Francis Beaufort, Knight Commander of
the Bath (1774-1857). Beaufort entered the Royal Navy at the age of 13 and by 1800
had risen to the rank of Commander. In the summer of 1805 Commander Beaufort was
appointed to the command of the Woolwich, a 44 gun man-of-war. It was at this time
that he devised his wind force scale. By 1838 the Beaufort wind force scale was
made mandatory for log entries in all ships of the Royal Navy.
In examining Beaufort's scale, it catches one's attention that the scale is is
a force scale. There is no mention of wind speed! Given the current applications
of the scale and the fact that meteorologist are generally unfamiliar with sailing
ships underway, it is easy to see that Beaufort's intentions in creating the scale
may be mistaken. Beaufort's specification is essentially an association of a set
of integers (0 to 12) with a description of the state and behavior of a "well-conditioned
man-of-war." While the choice of numbers is quite arbitrary, as a sailor Beaufort
apparently felt there were 13 levels of behavior that he could recognize in a man-of-war.
Although he describes them in terms that may be vague to a modern sailor, his descriptions
would certainly convey the full meaning of the force of the wind to men who shared
years of sailing in ships with characteristics similar to the Woolwich.
Beaufort force
- Light Air Or just sufficient to give steerage way.
- Light Breeze Or that in which a man-of-war with all sail set, and clean
full would go in smooth water from. 1 to 2 knots
- Gentle Breeze 3 to 4 knots
- Moderate Breeze 5 to 6 knots
- Fresh Breeze Or that to which a well-conditioned man-of-war could just carry
in chase, full and by. Royals, &c.
- Strong Breeze Single-reefed topsails and top-gal. sail
- Moderate Gale Double reefed topsails, jib, &c.
- Fresh Gale Treble-reefed topsails &c.
- Strong Gale Close-reefed topsails and courses.
- Whole Gale Or that with which she could scarcely bear close-reefed main-topsail
and reefed fore-sail.
- Storm Or that which would reduce her to storm staysails.
- Hurricane Or that which no canvas could withstand.
The effect of the wind on an 18th-century fighting ship is at the heart of Beaufort's
scale. Note that Beaufort intends that you look at the ship not at the wind! The
scale was devised for a group of men who shared the same experience -- years of
unremitting blockade of Europe in sailing ships which were all quite similar in
characteristics. His descriptions are couched in terms of the ship's characteristics
under sail.The descriptions for Beaufort numbers 0 through 4 describe the wind in
terms of the speed that it may propel the ship; those for 5 through 9 in terms of
her mission and her sail carrying ability; and those for 10 through 12 in terms
of her survival. So how then did Beaufort's wind force scale ever make the jump
to a wind speed scale?
Special wind scales had been routinely suggested through the years but their
lives were usually as short as mayflies'. What happened after 1838, when the Royal
Navy made Beaufort's scale mandatory, helps to explain its incredible longevity.
In one sense the story is a tale of the triumph of technology over rational thought.
It begins with a couple of gadgets -- in 1837 Samuel Morse demonstrated the first
practical telegraph and in 1846 T. R. Robinson invented the cup anemometer. Neither
of these inventions would have saved Beaufort's scale, however, if it weren't for
a catastrophe.
In 1854 the English and French were entrenched in fighting at Sevastopool. The
fleets carrying almost all their winter supplies was struck by an intense, early
winter storm on the morning of November 14. In 12 hours the English and French suffered
losses (no less than 21 supply ships by the British alone) that exceed the most
savage fleet action that had ever been fought. In response to the losses and with
the hope that there might be some way to forecast future storms, the British Admiralty
and the French Marine jointly sponsored a weather network -- the ancestor of the
World Meteorolgoical Organization -- to provide storm warnings. And here then is
when Sir Beaufort's scale begins its protean growth.
Since the task of forecasting storms was commissioned partly by the Royal Navy
for use by mariners and they had made the use of Beaufort numbers mandatory, it
"naturally" developed that Beaufort numbers would be used for a meteorolgoical purpose.
At the same time, meteorologists of the time were excited about the possibilities
of the new weather net and the deployment of anemometers everywhere. And how better
to code and telegraph this wealth of new wind information than Beaufort numbers!
Ah, but here the trouble begins. In central Europe a peasant who had never seen
the ocean, let alone an 1805 man-of-war, observed 37 revolutions of his anemometer
and, after looking up the equivalent in his conversion table, sent a Beaufort 7;
his cohort in Kansas, who had never seen the ocean either, looked up the same 37
revolutions in his table and sent it as a Beaufort 5. The confusion only increased
with the proliferation of more than 30 sets of wind speed equivalents by 1900 --
some disagreeing by more than 100 percent. It was no longer clear just what the
old force scale meant (and few men survived who were competent to judge what the
behavior of an 1805 man-of-war would be!).
In 1912 the International Commission for Weather Telegraphy sought some agreement
on velocity equivalents for the Beaufort scale. A uniform set of equivalents was
accepted in 1926 and revised slightly in 1946. By 1955, wind velocities in knots
replaced Beaufort numbers on weather maps. But there were still a need for eyeball
estimates by seamen to fill the gaps in the global observing network. Thus it became
imperative to relate the seaman's guess logged in Beaufort numbers to the wind speed
in knots. And so Beaufort's scale had transfomed itself from a tool of the mariner
to a means for the meteorologist!
Meteorologists set in motion the search to define a set of wind velocity equivalents
for the Beaufort force numbers. That the numbers were ever used to transmit anemometer
readings may well be one of those minor stories of history that has a much more
signifcant affect than warranted. If 100 years ago there had been a way to extend
weather observerations across the oceans using only the science of meteorology,
perhaps Admiral Beaufort's scale and numbers might have been buried long ago --
preferably at sea!
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