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Storm (Violent commotion)
a violent commotion or disturbance of the atmosphere, producing or attended by wind, rain, snow, hail, or thunder and lightning; a tempest; often applied to a heavy fall of rain, snow, etc., without a high wind. There is, perhaps, no question in science in which there was long so large an admixture of speculation with fact as in the attempts made to reduce the phenomena of storms under general laws; the reason being that meteorological observatories were too few in number and too wide apart to represent the barometer pressure, the general course of the winds, and the rainfall, without drawing largely on conjecture.
The extent over which storms spread is very variable, being seldom less than 600 miles in diameter, but often two or three times greater, and more rarely even five times that amount. More than the whole of Europe is sometimes overspread by a single storm at one time. The prime difference between storms or cyclones and tornados is that the breadth of the space traversed by the latter is, as compared with that of storms, always quite insignificant. The area of storms is not constant from day to day, but varies in size, sometimes expanding and sometimes contracting; and it is worthy of remark that when a storm contracts in area the central depression gives signs of filling up, and the storm of dying out. On the other hand, when it increases in extent the central depression becomes deeper, the storm increases in violence, and occasionally is broken up into two or even more depressions, which become separate storms, with the wind circling round each. This occurs frequently with summer thunderstorms.
Direction in Which Storms Advance.- The direction in which their progressive motion takes place differs in different parts of the world-being perhaps determined by the prevailing winds. Thus, about half the storms of middle and northern Europe travel from the S. W. toward the N. E., and about 19 out of every 20 travel toward some point in the quadrant lying between the N. E. and the S. E. Storms rarely travel toward a W. point; in some of the instances which have been noted the W. course has been arrested at Norway, Denmark, the North Sea, or the British Islands, but such W. course is temporary, the E. course being afterward resumed. Some of the most violent E. storms fall under this head. Storms do not always proceed in the same uniform direction from day to day, and, though the change which occurs in the direction of their progressive motion is generally small, yet occasionally it is very great. STORM The storms of the Mediterranean follow a different course. While a number take the general E. course of European storms, a larger number originate in the gulfs of Lyons and Genoa, and pursue devious courses over this N. extension of the Mediterranean, till they die out; several advance from Turkey and Greece toward the Alps; and others, comparatively few, advance in an E. course toward the Levant. By far the greater number of the storms of North America take their rise in the vast plain which lies to the E. of the Rocky Mountains, and thence advance in an E. direction over the United States, their course being largely determined by the Great Lakes; some of them cross the Atlantic, and burst on the W. shores of Europe. But the connection of the American with the European storms is not even yet well established. The storms of the West Indies generally take their rise somewhere N. of the region of calms, and, tracing out a parabolic course, proceed first toward the W. N. W., and then turn to the N. E. about lat. 30° N., not a few traversing the E. coasts of North America as far as Nova Scotia. South of the equator they follow an opposite course. Thus, in the Indian Ocean they first proceed toward the S. W., and then gradually curve round to the S. E. The hurricanes of India usually pursue a parabolic path, first traversing the E. coast toward Calcutta, and then turning to the N. W. up the valley of the Ganges.
The typhoons of the Chinese Sea resemble, in the course they take, the hurricanes of the West Indies. Rate at Which Storms Travel-The average rate of the progressive movement of European storms is about 162 miles per hour. From an examination of extensive series of storms Professor Loomis has shown that the average rates of progress of storm centers are in miles per hour 28 for the United States, 18 for the middle latitudes of the Atlantic Ocean, 17 for Europe, 15 for the West Indies, and 9 for the Bay of Bengal and China Sea. On Jan. 7-8, 1877, a storm traveled in 24 hours from Indianola, Tex., to Eastport, Me.-1,782 miles, or 78 miles an hour. On the other hand, the rate of progress is, particularly in the tropics, sometimes so slow as to be virtually stationary; and, as already stated, they occasionally recurve on their paths.
Relations of Temperature, Rain, and Cloud to Storms. - Temperature increases at places toward which and over which the front part of the storm is advancing, and falls at those places over which the front part of the storm has already passed. In other words, the temperature STORM rises as the barometer falls, and falls as the barometer rises. When the barometer has been falling for some time clouds begin to overspread the sky, and rain to fall at intervals; as the central depression approaches the rain becomes more general, heavy, and continuous. After the center of the storm approaches, or shortly before the barometer begins to rise, the rain becomes less heavy, falling more in showers than continuously; the clouds break up when the center has passed, and fine weather, ushered in with cold breezes, ultimately prevails. If the temperature begins to rise soon and markedly after the storm has passed, a second storm may be shortly expected.
Direction of the Wind. If the winds are examined, they will be observed whirling round the area of low barometer in a circular manner, and in a direction contrary to the motion of the hands of a watch, with a constant tendency to turn inward toward the center of lowest pressure, in the manner formulated in Buys-Ballot's law. The wind in storms neither blows round the center of lowest pressure in circles, nor does it blow directly toward that center, but takes a direction nearly intermediate, approaching, however, nearer to the direction and course of the circular curves than of the radii to the center. In the front of the storm the winds blow more toward the center, but in the rear they blow more closely approximate to the circular isobaric lines. Where the direction of the wind differs to any material degree from the above it is light, and consequently more under local influences, which turn it from its true course. In the Southern Hemisphere a rotary motion is also observed round the center of storms, but it takes place in a contrary direction, or in the direction of the motion of the hands of a watch, instead of contrary to that direction, as prevails N. of the equator.
Force of the Wind. The rule is simple, and without exception-viz., the wind blows from a high to a low barometer with a force proportioned to the barometric gradient or to the difference of the barometric pressures reduced to sea-level. Hence where the isobaric lines crowd together the violence of the storm is most felt, and where they are far asunder the winds are moderate, light, or nil. We thus see the importance of observations from a distance in forecasting the weather. The progressive motion of storms, which may vary from zero to 78 miles an hour, measures the time taken in passing from one place to another, but it gives no indication of the violence of STORM the storm. This is determined by the velocity of the wind round and inward on the center of the storm, which in Europe and the United States frequently amounts to 60 or 80 miles an hour continuously for some time. In intermittent gusts a speed of 120 miles an hour has been several times observed in Great Britain-a velocity which is perhaps sometimes surpassed by storms within the tropics. On the top of Ben Nevis higher velocities, rising to upward of 150 miles, are of not infrequent occurrence.
Causes of Cyclones. -Dove, who did so much in this department of meteorology, held the view that cyclones are formed when two great atmospheric currents, called polar and equatorial, flow side by side, storms being the eddies, as it were, formed along the line of junction. It is to be kept in mind that the qualities of the atmosphere in the front portion of a cyclone are quite different from those in the rear-the former being warm and moist, while the latter are cold and dry.
The conclusion is inevitable that the apparent rotation of winds in storms is simply a circulatory movement maintained between two currents, and that no mass of the same air makes the complete circuit of the cyclone.
Forecasting. - Valuable aid in forecasting storms and weather is derived from two important deductions from past observations: (1) A cyclone tends toward a path near to the anticyclone which lies immediately to the right of the progressive motion of the storm at the time. 2' When the rates of fall of the barometer at stations in the W. of Europe are noted, it is found that the path taken by the coming storm is indicated by those stations at which the rates of fall of the barometer are greatest. See METEOROLOGY.
Relations of Storms to the Character of the Season. - This is vital and allimportant. Thus, as regards the British Islands, when the general path pursued by storms in their E. course over Europe lies to the S. the winter is severe, inasmuch as the British Islands are then on the N. side of the center of low pressure, and consequently in the stream of the N. and E. winds which there prevail.
On the other hand, when the paths of storms lies to the N. the British Islands are on the S. side of the low pressure, and therefore in the stream of the warm, moist, S. and S. W. winds which there prevail.
It is plain that the character of the weather of any particular day or season is wholly determined by the way in which areas of high and of low atmospheric pressure are distributed over the region during that day or season. Fur- STORM ther, the weather of the coming season could certainly be predicted for say the British Islands, if only the general path was known which the centers of the Atlantic cyclones will take in their E. course over Europe; for if the paths of the winter storms be to the N. of Great Britain the winter will be an open one, but if to the S. a severe winter is the certain result. Toward the solution of this highly practical problem we look to seamen to put us in possession of a fuller and, above all, an earlier knowledge of the fluctuations of the surface temperature of the Atlantic, and to high-level observatories for the data required in obtaining a clearer insight into at into the history and theory of storms. See METEOROLOGY: WEATHER BUREAU: WIND:
CYCLONE.