| 单词 | cyclone | ||||||
| 释义 | cyclonecy·cloneC0835700 (sī′klōn′)cyclone(ˈsaɪkləʊn)Cyclone(ˈsaɪkləʊn)cy•clone(ˈsaɪ kloʊn)n. cy·clone(sī′klōn′)cyclonecyclone
cyclonecyclone(ˈsaikləun) nouncyclone→ 旋风zhCNcyclonecyclone,atmospheric pressure distribution in which there is a low central pressure relative to the surrounding pressure. The resulting pressure gradient, combined with the Coriolis effectCoriolis effect[for G.-G. de Coriolis, a French mathematician], tendency for any moving body on or above the earth's surface, e.g., an ocean current or an artillery round, to drift sideways from its course because of the earth's rotation. ..... Click the link for more information. , causes air to circulate about the core of lowest pressure in a counterclockwise direction in the Northern Hemisphere and in a clockwise direction in the Southern Hemisphere. Near the surface of the earth, the frictional drag on the air moving over land or water causes it to spiral gradually inward toward lower pressures. This inward movement of air is compensated for by rising currents near the center, which are cooled by expansion when they reach the lower pressures of higher altitudes. The cooling, in turn, greatly increases the relative humidity of the air, so that "lows" are generally characterized by cloudiness and high humidity; they are thus often referred to simply as storms. According to the theory first proposed by the Norwegian physicist Vilhelm BjerknesBjerknes, Vilhelm Frimann Koren Tropical cyclones, formed over warm tropical oceans, are not associated with frontsfront, Cyclones in middle latitudes move generally from west to east along with the prevailing winds and cover 500 to 1,000 mi (800–1,610 km) each day; tropical cyclones usually move toward the west with the flow of the trade winds during their formative stages, then curve toward the poles around subtropical anticyclonesanticyclone, BibliographySee D. Longshore, Encyclopedia of Hurricanes, Typhoons, and Cyclones (1998). Cyclonein industry, a device for removing suspended solid particles or droplets from air or a gas by means of centrifugal force (Figure 1). A dust-laden gas stream usually enters the upper cylinder of a cyclone through an inlet at high speed; the inlet may be situated at a tangent to the cylindrical surface of the cyclone or may be involute. As a result, the gas acquires rotational motion and spirals
from the top to the bottom, forming an outside vortex. As the gas spirals downward, the suspended particles are flung toward the walls of the cyclone by the inertial force. The particles spiral downward with the gas stream to the bottom of the cyclone and are then removed through a dust outlet. The cleaned gas spirals upward through an outlet pipe, forming an inside vortex, and leaves the device. Cyclones in which the gas enters axially are also used. In such devices, rotational motion is imparted to the gas stream by a guide vane, which may be a screw or an impeller with canted blades. The extent to which dust can be removed from a gas by a cyclone depends on the geometric dimensions and the shape of the cyclone, the properties of the dust, the velocity of the gas stream, and certain other factors. The collection of particles in a cyclone may be improved by increasing the velocity of the gas stream (the most effective velocities range from 20 to 25 m/sec) or by reducing the diameter of the cyclone. Therefore, an arrangement of several cyclones in parallel is used to obtain a high collection efficiency when a large amount of gas is to be cleaned. In cyclones of the most advanced design, particles with a diameter of 5 micrometers or larger may be collected with a sufficiently high efficiency. (See alsoLIQUID CYCLONE.) Cyclonean atmospheric disturbance characterized by low pressure at the center and vortical movements of air. A distinction is made between extratropical and tropical cyclones. The latter have special properties and occur less frequently (see). The barometric pressure in a cyclone is lowest at its center and increases toward the periphery; that is, the horizontal pressure gradients are directed from outside the cyclone inward. In a mature cyclone, the pressure at the center at sea level may drop to 960–950 millibars (1 bar = 105 newtons/m2) and occasionally down to 930–920 millibars; the average pressure at sea level is about 1,012 millibars. Closed isobars (lines of equal pressure), shaped like an irregular oval, bound the region of low pressure, which may be anywhere from a few hundred to 2,000–3,000 km in diameter and in which the air is moving in a vortex. In the free atmosphere, above the boundary layer, which is approximately the first 1,000 m, the air moves approximately along the isobars, deflecting from the pressure gradient at an angle close to 90° to the right in the northern hemisphere and to the left in the southern hemisphere; this occurs as a result of the Coriolis force and the centrifugal force that arises during movement along curved trajectories. In the boundary layer, the force of gravity causes the wind to deviate to some extent, depending on elevation, from the isobars toward the pressure gradient. At the surface of the earth, the wind and the pressure gradient form an angle of about 60°; that is, the flow of air toward the center of the cyclone is joined to the vortical movement of the air. The lines of flow resemble spirals, converging at the center of the cyclone. The wind velocities in a cyclone are greater than in adjacent regions of the atmosphere, sometimes reaching more than 20 m/sec (storm) and even 30 m/sec (hurricane). Cloudy weather predominates in a cyclone because of the ascending components of air movement, particularly near the fronts. Cyclones are responsible for most of the precipitation occurring in the extratropical latitudes. As a result of the vortical air movements, air masses of different temperatures from different latitudes of the earth are drawn into the cyclone region. The temperate differences within a cyclone are related to this. This applies particularly to traveling cyclones that occur along the main fronts of the troposphere (the arctic, antarctic, and polar fronts). Weak cyclones are also observed above the warm parts of the earth (deserts and inland seas). Called thermal lows, such cyclones are relatively immobile and have a fairly even temperature distribution. At higher elevations, the isobars of a cyclone gradually lose their closed form. This occurs in different ways, depending on the stage of development of the cyclone and the temperature distribution within it. In the first stage of development, a traveling (frontal) cyclone engulfs only the lower part of the troposphere, while at its stage of greatest development, it may spread through the entire troposphere and even extend into the lower stratosphere. Thermal lows are always restricted to the lower troposphere. Traveling cyclones generally move from west to east. The direction of movement of a given cyclone is determined by the direction of the general transfer of air in the upper troposphere. Movement in the opposite direction, that is, from east to west, is rare. The average velocity of a cyclone’s movement is 30–45 km/hr, but there are cyclones that move faster, up to 100 km/hr, especially in the initial stages of development. In the concluding stage, a cyclone may remain immobile for a long time. The movement of a cyclone through a certain region causes sharp and significant local changes not only in atmospheric pressure and wind but also in air temperature, humidity, cloudiness, and precipitation. Traveling cyclones usually develop along the main fronts of the troposphere, which have originated earlier; they are wave-like disturbances as the air flows along both sides of the front. Unstable frontal waves grow into cyclonic vortices. Moving along the front, which is usually extended latitudinally, the cyclone itself alters the front, giving rise to meridional components of the wind and thus promoting the transfer of the warm air in the forward (eastern) part of the cyclone toward the higher latitudes and the transfer of the cold air in the rear (western) part toward the lower latitudes. In the southern part of the cyclone, a warm sector, which is bounded by a warm front and a cold front, is created in the lower layers (the stage of a young cyclone). Then, when the cold and warm fronts merge (occlusion of the cyclone), the warm air is forced away from the earth’s surface by the cold air into the higher layers. The warm sector is eliminated, and a more even temperature distribution is established in the cyclone (the stage of an occluded cyclone). The reserve of energy capable of being converted into kinetic energy runs out in the cyclone, and thus the cyclone dissipates or merges with another cyclone. A series, or family, of cyclones, consisting of several cyclones moving one after another, usually develops along a main front. At the end of the series’ development, individual cyclones that have not yet dissipated merge together into a vast, relatively immobile, deep, and high central cyclone consisting of cold air throughout its height. This cyclone also gradually dissipates. Anticyclones, with high pressure at the center, develop between cyclones at the same time as the cyclones form. The entire process of a particular cyclone’s development takes several days; a cyclone series and the main cyclone may exist for one or two weeks. At any given moment, there are several main fronts and the cyclone series associated with them in each hemisphere; the total number of cyclones in a given year runs into several hundred over each hemisphere. There are certain latitudes and regions in which the formation of main fronts and frontal disturbances occurs quite regularly. As a result, there are certain geographic regularities in the frequency of occurrence and movement of individual cyclones and anticyclones and cyclone and anticyclone series; that is, there exist patterns of cyclonic activity. However, the effects of land and sea, topography, orography, and other geographical factors on the formation and movement of cyclones and anticyclones and their interaction make the general picture of cyclonic activity quite complex and fast-changing. Cyclonic activity leads to interlatitudinal exchange of air, movement, heat, and moisture, which makes it important in the atmospheric general circulation. REFERENCESPalmén, E., and C. Newton. Tsirkuliatsionnye sistemy atmosfery. Leningrad, 1973. (Translated from English.)Petterssen, S. Analiz i prognoz pogody. Leningrad, 1961. (Translated from English.) Khromov, S. P. Osnovy sinopticheskoi meteorologii. Leningrad, 1948. Zverev, A. S. Sinopticheskaia meteorologiia i osnovy predvychisleniia pogody. Leningrad, 1968. Pogosian, Kh. P. Tsiklony. Leningrad, 1976. S. P. KHROMOV cyclone[′sī‚klōn]cyclone cycloneCycloneNatural disaster A large-scale closed circulation atmospheric system that develops above the Indian Ocean and South Pacific with low barometric pressure and strong winds—64+ knots/hr—that rotate clockwise cyclone
Synonyms for cyclone
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cyclone - (meteorology) rapid inward circulation of air masses about a low pressure center; circling counterclockwise in the northern hemisphere and clockwise in the southern