Beaufort scale
The Beaufort scale is a scale for the classification of winds according to their speed. It is the most widely used system for the description of wind speed. It is named after Sir Francis Beaufort, but he has had only a small part of its development. The colloquial term wind speed for the classification according to the Beaufort scale is used especially by lay very vague and can the Beaufort scale mine, but also wind speed ( "Wind speed ten knots " ), wind turbines ( " wind force ten Newton" ), wind pressure ( " wind force ten kilograms per square " ) or the perceived strength of the wind (low wind speed, storm wind strength, etc.). In the Marine, Aviation and Meteorology is with wind strength always an integer value on the Beaufort scale meant, unless it is expressly stated to a different scale, such as a hurricane or tornado scale.
The terms wind strength and force of the wind can be clearly distinguished from each other. In technical texts such as weather forecasts or logbooks using the Beaufort scale is not mentioned, but provided no statement of the wind strength is without unit: SW5 -6 wind force five to six, spoken as a southwest wind of ( Beaufort scale ) "Southwest five to six ." The wind speed is traditionally given in nodes, slowly in the modern meteorological research papers m / s penetrates and is used in general publications such as TV weather forecasts, mostly km / h.
- 4.1 diagram
Scope
Between wind speed and Beaufort Force B ( rounded ) consists after the revision of the Beaufort scale in 1946 the following relationship:
Or resolved to B:
Where v is the wind speed is 10 meters above the surface. The first of the formulas was established in 1913 by the British weather service as a national standard and proposed as an international standard in 1914 ( the proposal was rejected ). It is based on an examination of the later Weather Service Director Sir George Clarke Simpson from 1905 /6, which was not published on the basis of miles per hour. Approximated For other units:
Or
A simplified connection is:
( This approach leads in winds 3-10 Bft errors < 0.5 Bft. However, under practical conditions and measurements with commercially available devices, this error is usually negligible. )
Since it is unusual to work with fractions or decimal fractions of wind speeds, it is necessary to calculate the lower and upper bounds of the integer wind speeds according to one of the above formulas. In this case, the limit values in the units node, km / h and Mph on integers and the values in m / s to exactly one decimal place. Upper limits are off, lower bounds are rounded up. Force 9 Bft, ie B 8.5 to 9.4 thus corresponds to a wind speed of 20.7 to 24.4 m / s, corresponding to 10 Bft from 24.5 to 28.4 m / s, etc.
In fact, the calculation formula only the " lowest common denominator " that in the experiments at numerous international meteorological and geophysical conferences between 1914 ( in Rome) and 1970 to create a common basis for a uniform weather forecast, because since the sinking of the Titanic every seafaring nation was obliged to disseminate current weather reports to their coasts. Subject of negotiations was in addition to the limit tables even the particular measurement method, changing measurement heights or measurement times and other formalities. Agreement was achieved for the first time in 1926 with the Vienna scale that was calculated from the arithmetic mean values of the British Simpson scale and the international spread, older scale of the German Naval Observatory in Hamburg. In 1946 it was assumed that Simpson scale of 1906 and 1913 as a so-called Parisian scale, and then to expand it in 1947 after the calculation formula up to wind force 17 for the description of the hurricane. This was in 1949 with the determination, wind speeds have to be measured in knots, as Washington confirms code. In 1960, the expansion to 17, even temporarily withdrawn unofficially on 23 winds, as the aviation was completely dropped out of the Beaufort scale, meteorology developed its own hurricane scale and the seafaring got along with 12 wind strengths.
In extreme cases or for storms on other planets, such as Mars, the wind speed is specified directly in an appropriate unit.
The wind pressure increases with the square of the wind speed, and thus with the cube of the Beaufort wind strength. Since the Beaufort scale but only the rate and not dependent on the amount and temperature of air density into account, the allocation of Beaufort wind force and wind pressure is not unique. A storm with eg Beaufort 11 on a 6000 meter high mountain developed only about half the wind pressure as a storm of the same Beaufort Force at sea level.
The wind speeds given in weather maps and weather reports do not refer to the peak gusts (which can be twice as strong light), but on a 10-minute average. Of these, the procedure differs in the weather forecast, especially the Seewettervorhersage and wind forecast. Here the winds of the expected, the strongest gusts are specified for liability reasons. For example, the German Weather Service loud Typical formulations: " Forecast for the German Bight. Northwest to West 4 to 5 individual shower squalls " It squalls, the term refers, first, to possible rain, secondly for possible vision disabilities and thirdly, that the Seewetterdienst from any wind speed forecast dissociates under clouds. In public broadcasters broadcasting, such as the Germany radio, the latter is misleading translated at a flat gusts surcharge of one to two winds: " The Seewetterdienst Hamburg announces: German North Sea coast: South East to West 6, gusts to 8 German Baltic Sea Coast: West 6-7, gusting up to 9 " the wind forecast in the context of different " television weather reports " raises are generally not entitled to quantitative accuracy, but is intended to illustrate the consumer whether to expect more or less wind. However, this is due to circumstances that an accurate local wind forecast over 24 hours by a single number with global methods is already practically impossible and that the "Weather presentation " to have a predominantly entertaining character after the political and sports news.
In search of what might have next to the square of the pressure the third power in the formula for a practical meaning, one comes across the moment of resistance in cross-section bending -loaded rods. It varies with the cube of the diameter for round or radius of gyration with arbitrary cross sections. This results in the sense of Beaufort to the practical- philosophical and also transmissible to land objects, albeit shortened by other conditions, concluded that in the same Sails breaks double wind strength double pole diameter.
History
The Beaufort scale is not from Francis Beaufort ( 1774-1857 ). Already Tycho Brahe had tried to categorize the winds. The engineer John Smeaton characterized them for the first time through their effect on windmill blades. His 1759 published table contained eleven winds ( wind not counted), each wind strength he described by its effect on the environment, such that a hurricane outlier trees and destroy buildings. These he gave to each of the wind speed and wind pressure. In a manuscript from 1790 Smeaton's scale is grouped into nine winds, which were characterized by their effects on a windmill. So was a " breeze " as defined in that they could move the branches of a tree and a mill wings per minute put back six to nine turns.
From large retail companies such as the East India Company and the Navy logbooks of the returning captains were systematically evaluated to Beaufort's time, among other things, instructions to get to favorable wind conditions. The then usual comments like " moderate wind " were not standardized and therefore not comparable. The problem was that the wind at sea - on board a sailing ship that was moving along with the wind - could not be measured directly and in itself was invisible. Various researchers have attempted, therefore, to characterize the wind by its effects.
The former Hydro Count the "East India Company " and 1795 First Hydro Count of the Admiralty, Alexander Dalrymple, Smeaton's scale made known in seafaring. Dalrymple's version contained twelve winds ( again with no wind), the one of "weak draft " to 12 " storm" ranged. Dalrymple published his own scale, which was specifically designed for use in logbooks, 1779 in a brochure and 1790 in the book Practical Navigation.
Beaufort learned Dalrymple scale probably already know by its brochure from 1779. Throughout his life he led an extensive diary in which he recorded the weather among other things. On 12 or 13 January 1806 he was here the words of one: " From now on I will appreciate the strength of the wind according to the following scale, because nothing conveys a more unclear idea of wind and weather than the old expressions moderate and cloudy, etc. etc. "It follows a scale of 1 to 13, from" "to " storm " is enough wind. On September 14, 1807, he put on a new diary, in which he - as usual - on the flyleaf of the wind scale quoted, which he intended to use. Shortly thereafter, he improved the scale by adding how the wind strength was recognized by the sailing a full-rigged frigate. So there is some wind force 5 if topsail, topgallant, royal, flyers and staysail can remain hoisted at wind force 7, the top three sails must be reefed.
After Beaufort had become 1829 Hydro Count of the Admiralty, he gave his improved scale on to all who were interested in it. It was published in 1832 in the Nautical Magazine of the Admiralty. 1837 the scale has been used already in the whole survey service, and late 1838 gave the Admiralty a statement out, with which it was made compulsory. However, this scale was no name has been referred to merely as "the attached scheme ." Even in the full obituaries on the occasion of the Beaufort wind scale, a death is mentioned at any point.
Until 1906, created the British weather service, the version of the scale with 13 levels ( including 0 ), which has become known as the Beaufort scale ( in the following table together with the scale of the column " effect on land "). Here is some wind strength 0, ie no wind, characterized by the fact that smoke rises vertically. Wind-Force 2, a "light breeze ", the wind on his face felt and leaves will rustle. For this purpose, the respective wind speed is specified. In this version, the Beaufort scale has been included in numerous dictionaries and encyclopedias. 1927 formulated by the German captain Peter Petersen to the original scale of Beaufort for purposes of navigation, because sailing in shipping did not play a large role. In the Petersen swell scale the effect of the wind is described on the lake ( in the table, together with the scale of the column " effect on the sea ", also see the following images ). Thus, " strong wind " big waves from 2.5 to 4 meters in height, everywhere are extensive white foam crests to see form at wind force 6; there is some froth.
In 1935, the Beaufort scale was adopted at the First International Meteorological Conference in Brussels as universally valid. In 1949 the scale has been expanded by decision of the International Meteorological Organization to the following five to 18 levels (including 0 ) as an autonomous Saffir -Simpson Hurricane Scale:
- Wind Force 12: Wind speed: 118-133 km / h, instead of > 117
- Wind force 13: Wind speed: 134-149 km / h
- Wind force 14: Wind speed: 150-166 km / h
- Wind force 15: Wind speed: 167-183 km / h
- Wind force 16: Wind speed: 184-202 km / h
- Wind force 17: Wind speed: > 202 km / h
In 1970, the successor organization to the World Meteorological Organization reintroduced the old 12 - part scale. From the Beaufort scale - that is, together with the description by phenomenological criteria - there is no authoritative version, so it is used in many different variants. Professional meteorologists measure the wind speed with an anemometer directly and rely only in an emergency on the Beaufort scale.
Published in 1971 Theodore Fujita of the University of Chicago for wind speeds that go beyond the Beaufort scale, the Fujita Tornado Scale of F0 to F5. In this wind strength even paved roads can be " sucked" from the floor. Moreover, even the Saffir -Simpson Hurricane Scale in use, which divides hurricanes into five categories. The Japan Meteorological Agency and the Regional Specialized Meteorological Centres both in the northern and southwestern Indian Ocean apply them to different cyclone scales. Tropical Cyclone Warning Center, the local use at the scale of the Australian Bureau of Meteorology for the Southern Pacific and the Australian region; this is based on an extension of the Beaufort scale.
Beaufort Scale by phenomenological criteria
Pictures
- 1 Beaufort
- 2 Beaufort
- 3 Beaufort
- 4 Beaufort
- 5 Beaufort
- 6 Beaufort
- 7 Beaufort
- 8 Beaufort
- 9 Beaufort
- 10 Beaufort
- 11 Beaufort
- 12 Beaufort