Online Encyclopedia
Search over 40,000 articles from the original, classic Encyclopedia Britannica, 11th Edition.
WIND
Online EncyclopediaEncyclopedia Home :: WIL-YAK
del.icio.us it!
|
WIND VE
Mist. la.m.
Direr See also:ion
See also:succession of squalls of this See also:kind is a See also:common experience with , See also:westerly wind at Scilly, and the onset of squalls is generally associated with the veering of the wind to the See also:north-See also:west. Changes in wind velocity, either in the See also:form of gusts or squalls, are generally associated
See also:August a' 1 with some See also:change in direction of the
r u s ,o 11 MIOT. wind, but the relation between the changes in gusts have not yet been studied.
A characteristic of squalls is the
suddenness with which the increase
of wind velocity occurs. At See also:sea
the ruffling of the See also:surface can be
seen travelling over the See also:water, and
the wind producing it and travel-
See also:ling with it strikes a sudden See also:blow
° when it reaches a See also:ship. If squalls
are of sufficient violence to do damage to trees or buildings their progress can be traced in a like manner over the See also:land.
These phenomena are exhibited in their most striking form in " See also:line squalls." The characteristic feature of a line See also:squall is that a number of places arranged, roughly speaking, in a straight or slightly curved line across the See also:country experience a similar sequence of
,o events at the same See also:time, and the line of See also:action sweeps across the country as a front advancing nearly uniformly throughout its length. This See also: The squall often exhibits greater violence in the See also:middle portion, and it becomes more intense as the whole line advances. In the most fully See also:developed portions the See also:weather phenomena take the form of thunderstorms with violent wind and rain. The course of events in a typical line squall has been most care-fully worked out by R. G. K. Lempfert in a See also:paper on the " Line Squall " of the 8th of See also:February 1906 (Quart. Journ. See also:Roy. Met. See also:Soc. vol. xxxii.). Fig. 4 (reproduced from the papers) shows the successive positions of the line of the front from which its See also:rate of travel can be estimated. The line of advance of a line squall is generally from some point between See also:south and north on the western See also:side, the change of wind being from a warm southerly or westerly wind to a colder westerly or northerly one. So far as is known to the writer there is no See also:case of a line squall exhibiting a backing wind. The date and direction of advance appear to be, generally speaking, those of the final wind, but in cases where the thunderstorms are developed there is a See also:local violence of the wind bearing no relation to the isobaric See also:distribution of the final wind. Endeavours have been made to explain the phenomena of line squalls as due to vortex See also:motion of particular See also:character. The violent wind blowing out in front of the See also:storm is See also:part of the circulation of a vortex with See also:horizontal See also:axis. It supplies the See also:air for the rainfall of the stations in front. Its See also:place is taken by descending air at the back, which becomes in its turn the surface See also:supply for stations farther in. But such an explanationseems in many ways incomplete. Although perhaps if the wind velocities in a See also:vertical See also:plane were plotted there might be some See also:evidence of circulation in the mathematical sense by integrating See also:round a closed See also:curve, yet the See also:idea of circulation in a vertical plane as suggesting the See also:primary constitution of the phenomena is very inadequate. The change of air which takes place during the passage of the line squall is altogether different from that which we would get by passing the surface air through a See also:complete vertical See also:cycle and condensing a large quantity of water vapour on the way. If vertical circulation were complete the air would ° {e° ° ,Y 12 9 IB `1110 ~1 I 58 See also:INN , nit See also:milo,ripot iItqIimrIiIi,. A rxlljF'i, /geA ~`\ 0r 170 5 ,1 O 3 2 X70. 1f i_ 2.1d4I a•] R ~ ij • R9 i T MI 4 0 v. 4a, See also:mIn return to the surface warmed and dried. A few revolutions would produce a very considerable See also:elevation of temperature. The air which remains after the passage of a line squall is, how-ever, distinctly colder, of an entirely different kind from that which it replaces and, in those cases which have been investigated, can be traced back to a different point of the See also:compass. More-over, the smallness of vertical dimensions in the See also:atmosphere as compared with the horizontal dimensions makes it difficult to allow that there is really See also:room for an effective vortex with a horizontal axis. To carry air up 5 M. and bring it back again would practically deprive it of all its moisture and raise its temperature 72° F. Yet 5 M. would be a very small See also:allowance for the horizontal spread of the phenomena of the squall. The sudden replacement of warm air by See also:cold with a change of wind seems much more likely to be associated with the flooding of the country by an advancing sweep of cold air. The pressure changes are continuous in the old layer and in the new layer, but discontinuous with varying degrees of discontinuity along the line of junction, where instability of the upper air may be set up. Fig. 5 shows the discontinuity of pressure in the example discussed by Mr Lempfert. It is clear that as the discontinuity of pressure becomes accentuated there arise 80 70 NW w SW s SE 8 200 50 100 80 89 20 7 8 9 10 11 MIDI. (Redrawn by permission from the See also:British Association See also:Report,' 9o8.) Feb.B,i p.m.m' 2 . Feb.8,3 p.m. (95) 28.0 ; ~~ 28.9 29.1 • Y8.0 28• ` 28°4 20.3 za•~ 20.2 29• ~`' 29.3 28.3 ~ 29.8 28.8 28.7 29.1 r 28•3 29.8 ~ ~ ~) 29•. _ 30.0 28.8 ~ 2B•. ~ ~ 30• ~.. ~-111,.1; 3• Feb.8 a p.m. 14) 28,9 / 291.0 'Y9 WM 4Y. 29. 29• 29.3 , N. y 29.4 ~o 29 5 t 26.6 29.7 29 '4'ti ' 29.9 Y9j6 yyy • 19 58 30• 195 ”,o M g 3 '. 1_•8' 9.53 ~,,~~ • • 615 ~I~~. 44 6 951 r ''n •960 ¢ 36 3I1 So ~ 1 80.1 so• s• ,0 5" 0 5° o 1S" (Redrawn by permission from the Quart. Journ. Roy. Met. Soc.) are shown for each o'1 in. in the localities on the line of advance very steep pressure gradients for which there are corresponding winds. The violent winds may therefore be attributed to the breakdown of the dynamical See also:system under the stress of these local See also:differences of pressure. From this point of view the phenomena of the line squall are to be regarded as a development of the See also:ordinary phenomena of the V-shaped depression. A sudden change of wind and a line of rain that pass over the country with the velocity of the same • See also:order as that of the following wind are quite common features of the S.W. quadrant of a cyclonic depression, and they, too, seem to point to the juxtaposition of currents of different temperature coming from different regions but forming adjacent components of • supply for the depression. Examples of all degrees between the comparatively unimportant rain line • and the most violent See also:tornado-like • squall could be put side by side with cases in which the typical pressure, temperature and weather changes are (Redrawn by permission from accompanied by a sudden See also:lull in the the British Association Report, wind, as in the example quoted in the qo8.) wind velocity on See also:June 1, (M. O. publication, No. 174, 1906). 1908. An example of a line squall in its most violent and destructive form is shown in the records for the 1st of June 1go8. In the See also:record for See also:Kew the squall of wind which destroyed a number of the trees of Bushey See also:Avenue is shown as lasting for a very long See also:period (fig. 6). A line squall of historic See also:interest is that which capsized H.M.S. " See also:Eurydice " off the Isle of See also:Wight on the 24th of March 1878. The occurrence is discussed by the Hon. See also:Ralph See also:Abercromby in 1884 (Quart. Journ. Roy. Met. Soc. x. 172) and previously by the Rev. Mr Clementhey (Symon's Met. Mag., See also:April 1878). The shift of wind in this case appears to have been from west to north, and the change in the wind was accompanied by the transitions from See also:fine See also:blue See also:sky to snow. The records at the seven observatories belonging to the Meteorological See also:Council are reproduced in the Quarterly Weather Report, from which fig. 7 is taken.
Whatever explanation may be given of the cause and origin of the phenomena of line squalls, it must take See also:account of the fact that a first squall is often succeeded by others of a similar character but often of less intensity than the first. After the sudden shift of wind, with accompanying weather changes, the conditions seem to revert more or less to the See also:original See also:state. The warm southerly wind reasserts itself, but is driven out again by another attack, and ultimately the cold wind holds the See also: Additional information and CommentsThere are no comments yet for this article.
» Add information or comments to this article.
Please link directly to this article:
Highlight the code below, right click, and select "copy." Then paste it into your website, email, or other HTML. Site content, images, and layout Copyright © 2006 - Net Industries, worldwide. |
|
|
[back] WINCKELMANN, JOHANN JOACHIM (1717-.1768) |
[next] WIND (a common Teut. word, cognate with Skt. vats, ... |