Beaufort scale - Wikipedia, the free encyclopedia
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Beaufort scale
From Wikipedia, the free encyclopedia
The Beaufort scale (pronounced /ˈboʊfərt/) is an empirical measure for
describing wind speed based mainly on observed sea conditions. Its full name
is the Beaufort wind force scale.
Contents
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1 History
2 The modern scale
3 See also
4 References
5 External links
Force 12 at sea.
History
The scale was created in 1805 by Sir Francis Beaufort, an Irish-born British admiral and hydrographer. The
scale that carries Beaufort's name had a long and complex evolution, from the previous work of others, to
when Beaufort was a top administrator in the Royal Navy in the 1830s. In the early 19th Century, naval
officers made regular weather observations, but there was no standard scale and so they could be very
subjective - one man's "stiff breeze" might be another's "soft breeze". Beaufort succeeded in getting things
standardized.
The initial scale of thirteen classes (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." [1] At zero, all his sails would
be up; at six, half of his sails would have been taken down; and at twelve, all sails would be stowed away.[2]
The scale was made a standard for ship's log entries on Royal Navy vessels in the late 1830s and was adapted
to non-naval use from the 1850s, with scale numbers corresponding to cup anemometer rotations. In 1906, to
accommodate the growth 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 standardized only in 1923. George
Simpson, Director of the UK Meteorological Office, was responsible for this and for the addition of the landbased descriptors.[3] The measure was slightly altered some decades later to improve its utility for
meteorologists. Today, many countries have abandoned the scale and use the SI-based units m/s or km/h
instead, but the severe weather warnings given to public are still approximately the same as when using the
Beaufort scale.
The Beaufort scale was extended in 1946, when Forces 13 to 17 were added.[4] However, Forces 13 to 17 were
intended to apply only to special cases, such as tropical cyclones. Nowadays, the extended scale is only used in
Taiwan and mainland China, which are often affected by typhoons.
Wind speed on the 1946 Beaufort scale is based on the empirical formula:[5]
v = 0.836 B3/2 m/s
where v is the equivalent wind speed at 10 meters above the sea surface and B is Beaufort scale number. For
example, B = 9.5 is related to 24.5 m/s which is equal to the lower limit of "10 Beaufort". Using this formula
the highest winds in hurricanes would be 23 in the scale.
Today, hurricane force winds are sometimes described as Beaufort scale 12 through 16, very roughly related to
the respective category speeds of the Saffir-Simpson Hurricane Scale, by which actual hurricanes are
measured, where Category 1 is equivalent to Beaufort 12. However, the extended Beaufort numbers above 13
do not match the Saffir-Simpson Scale. Category 1 tornadoes on the Fujita and TORRO scales also begin
roughly at the end of level 12 of the Beaufort scale but are indeed independent scales.
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Beaufort scale - Wikipedia, the free encyclopedia
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Note that wave heights in the scale are for conditions in the open ocean, not along the shore.
The modern scale
Beaufort
Description
number
Wave
height
Wind speed
km/h mph kts m/s
<
0
0.3
<1
1
Light air
0.3
1.1 –
1–
0–
1–3
–
5.5
2
0.2
1.5
Ripples
0–
without
1
crests.
1.6 0.2
5.6 –
3–
4–7
–
–
11
6
3.4 0.5
Small
wavelets.
1 – Crests of
Wind felt on exposed
2
glassy
skin. Leaves rustle.
appearance,
not breaking
3
4
5
6
3.4
7–
0.5
–
10
–1
5.4
0
Flat.
Large
wavelets.
2 – Crests begin
3.5 to break;
scattered
whitecaps
Wind motion visible in
smoke.
Leaves and smaller
twigs in constant
motion.
Gentle
breeze
12 – 8 –
19
12
Moderate
breeze
11 5.5
20 – 13 –
1–
– –
28
17
2
15 7.9
Small waves
with breaking Dust and loose paper
3.5
crests. Fairly raised. Small branches
–6
frequent
begin to move.
white horses.
16 8.0
29 – 18 –
2–
– –
38
24
3
20 10.7
Moderate
waves of
some length. Branches of a moderate
6–
Many white size move. Small trees
9
horses. Small begin to sway.
amounts of
spray.
21 10.8
39 – 25 –
3–
– –
49
30
4
26 13.8
Long waves
begin to
form. White
foam crests
9 – are very
13 frequent.
Some
airborne
spray is
present.
50 – 31 –
61
38
Sea heaps up.
Some foam
13 – from
19 breaking
waves is
blown into
streaks along
Fresh
breeze
Strong
breeze
7
High wind,
Moderate
gale, Near
4–
5.5
27 13.9
– –
http://en.wikipedia.org/wiki/Beaufort_scale
Sea state
photo
Calm. Smoke rises
vertically.
Calm
Light
breeze
<1
ft
Land conditions
0
2
<1
m
Sea
conditions
Large branches in
motion. Whistling
heard in overhead
wires. Umbrella use
becomes difficult.
Empty plastic garbage
cans tip over.
Whole trees in motion.
Effort needed to walk
against the wind.
Swaying of skyscrapers
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Beaufort scale - Wikipedia, the free encyclopedia
gale
8
33 17.1
34 17.2 5.5
Gale, Fresh 62 – 39 –
– –
–
gale
74
46
40 20.7 7.5
41 20.8
75 – 47 –
7–
– –
88
54
10
47 24.4
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wind
direction.
Moderate
amounts of
airborne
spray.
may be felt, especially
by people on upper
floors.
Moderately
high waves
with breaking
crests
forming
spindrift.
17.2 Well-marked
–
streaks of
20.7 foam are
blown along
wind
direction.
Considerable
airborne
spray.
Some twigs broken
from trees. Cars veer
on road. Progress on
foot is seriously
impeded.
High waves
whose crests
sometimes
roll over.
Dense foam
is blown
along wind
23 –
direction.
32
Large
amounts of
airborne
spray may
begin to
reduce
visibility.
Some branches break
off trees, and some
small trees blow over.
Construction/temporary
signs and barricades
blow over. Damage to
circus tents and
canopies.
9
Strong gale
10
Very high
waves with
overhanging
crests. Large
patches of
foam from
wave crests
give the sea a
48 24.5
white
[6]
89 – 55 –
9 – 29 –
Storm ,
– –
appearance.
Whole gale 102 63 55 28.4 12.5 41 Considerable
tumbling of
waves with
heavy
impact. Large
amounts of
airborne
spray reduce
visibility.
Trees are broken off or
uprooted, saplings bent
and deformed. Poorly
attached asphalt
shingles and shingles in
poor condition peel off
roofs.
Exceptionally
high waves.
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Beaufort scale - Wikipedia, the free encyclopedia
11
12
Violent
storm
Hurricane
[6]
103
–
117
≥
118
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Very large
patches of
foam, driven
before the
wind, cover
much of the
56 28.5
64 –
11.5 37 – sea surface.
– –
72
– 16 52 Very large
63 32.6
amounts of
airborne
spray
severely
reduce
visibility.
≥ 73
≥ ≥
≥
≥ 14
64 32.7
46
Huge waves.
Sea is
completely
white with
foam and
spray. Air is
filled with
driving spray,
greatly
reducing
visibility.
Widespread damage to
vegetation. Many
roofing surfaces are
damaged; asphalt tiles
that have curled up
and/or fractured due to
age may break away
completely.
Very widespread
damage to vegetation.
Some windows may
break; mobile homes
and poorly constructed
sheds and barns are
damaged. Debris may
be hurled about.
The scale is used in, and may be most recognizable to some from, the Shipping Forecasts broadcast on BBC
Radio 4 in the United Kingdom.
This scale is also widely used in China, Taiwan, Hong Kong and Macau, however with some differences
between them. Taiwan uses the Beaufort scale with the extension to 17 noted above. China also switched to
this extended version without prior notice on the morning of May 15, 2006[7], and the extended scale was
immediately put to use for Typhoon Chanchu. Hong Kong and Macau however keep using Force 12 as the
maximum.
In the United States, winds of force 6 or 7 result in the issuance of a small craft advisory, with force 8 or 9
winds bringing about a gale warning, force 10 or 11 a storm warning ("a tropical storm warning" being issued
instead of the latter two if the winds relate to a tropical cyclone), and force 12 a hurricane warning. A set of red
warning flags (daylight) and red warning lights (night time) is displayed at shore establishments which
coincide with the various levels of warning.
In Canada, maritime winds forecast to be in the range of 6 to 7 are designated as "strong"; 8 to 9 "gale force";
10 to 11 "storm force"; 12 "hurricane force". Appropriate wind warnings are issued by Environment Canada's
Meteorological Service of Canada: strong wind warning, gale (force wind) warning, storm (force wind)
warning and hurricane force wind warning. These designations were standardized nationally in 2008, whereas
"light wind" can refer to 0 to 12 or 0 to 15 knots and "moderate wind" 12 to 19 or 16 to 19 knots, depending on
regional custom, definition or practice. Prior to 2008, a "strong wind warning" would have been referred to as
a "small craft warning" by Environment Canada, similar to US terminology. (Canada and the USA have the
Great Lakes in common.) However, there being no generally accepted definition of "small craft", and to have
consistency between wind speed ranges and their associated warnings, the term "strong wind warning" has
become the national Canadian norm.
It is recommended that no water sport activities should continue in force 7 or above.[8]
See also
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American Practical Navigator
Saffir-Simpson Hurricane Scale
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Douglas Sea Scale
Enhanced Fujita Scale
Fujita scale
TORRO scale
CLIWOC
Sea state
References
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Huler, Scott (2004). Defining the Wind: The Beaufort Scale, and How a 19th-Century Admiral Turned
Science into Poetry. Crown. ISBN 1-4000-4884-2.
1.
2.
3.
4.
5.
^ Oliver, John E. (2005). Encyclopedia of world climatology. Springer.
^ BBC - Weather Centre - Features - Understanding Weather - Beaufort Scale
^ Met Office: The Beaufort scale at the Internet Archive
^ Walter J. Saucier (1955). Principles of Meteorological Analysis. Retrieved on 2009-01-09.
^ Tom Beer (1997). Environmental Oceanography. CRC Press. ISBN 0849384257. http://books.google.com/books?
id=pgZtaB-qOmYC&pg=PA224&dq=%22Beaufort+Scale%22+0.836&lr=&as_brr=3&ei=zE8R_qDAYjAiwHXs93VBQ&sig=-BYb90BCgJH9eCxqj5FDLJYk3kY.
6. ^ a b The names "storm" and "hurricane" on the Beaufort scale refer only to wind strength, and do not necessarily
mean that other severe weather (for instance, a thunderstorm or tropical cyclone) is present. To avoid confusion,
strong wind warnings will often speak of e.g. "hurricane-force winds".
7. ^ 昨日实行新标准“珍珠”属强台风_新闻中心_新浪网
8. ^ Water Sports Activity Logbook. LCSD, Hong Kong
External links
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UK Meteorological Office: The Beaufort Scale
Investigating Clouds, a lesson plan from the National Science Digital Library that uses the Beaufort
Scale.
Radio interview with Scott Huler.
OceanWeather.com gives current graphics for wind, waves and temperature
Open Source Textbook at Oceanworld.tamu.edu cites the original definition formula in chapter 4
Howtoons Poster showing effects on land/sea effects at each step.
US Economic Costs of High Winds NOAA Economics
Online calculator: Beaufort scale
The Weather Legacy of Francis Beaufort — The history of the Beaufort Scale.
Ireland's Beaufort was Windscale Inventor - by Dr John de Courcy Ireland
Retrieved from "http://en.wikipedia.org/wiki/Beaufort_scale"
Categories: Scales | Wind
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