- 行业: Weather
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The American Meteorological Society promotes the development and dissemination of information and education on the atmospheric and related oceanic and hydrologic sciences and the advancement of their professional applications. Founded in 1919, AMS has a membership of more than 14,000 professionals, ...
1. In general, a broad cloud formation that is not more than four times as long as it is wide. 2. In synoptic meteorology, the principal cloud structure of a typical wave cyclone, that is, the cloud forms found on the cold-air side of the frontal system. The maximum areal coverage is usually found over the region in advance of the warm front, and the minimum behind the cold front. Within the area of the cloud shield, there is an idealized but smaller precipitation shield.
Industry:Weather
1. As used in the U. S. National Weather Service, a rapid fall in temperature within 24 hours to temperatures requiring substantially increased protection to agriculture, industry, commerce, and social activities. Therefore, the criterion for a cold wave is twofold: the rate of temperature fall, and the minimum to which it falls. The latter depends upon region and time of year. 2. Popularly, a period of very cold weather.
Industry:Weather
1. Broadly, a power ratio used in certain applications of radar that describes the degree to which the backscattered power from unwanted targets (clutter) is suppressed or canceled in one mode of measurement relative to another mode of measurement. It is defined to yield a value greater than unity or, equivalently, a positive decibel quantity. For example, in some applications it is defined as the ratio of signal intensity backscattered from rain observed with linear polarization to the signal intensity backscattered from rain observed with circular polarization. Values of 25–30 dB are typical of light rain observed at wavelengths of 3– 10 cm. 2. For a dual-channel radar, the ratio of the power received in the orthogonal channel to that received in the transmission channel for transmitted circular polarization. The stronger component of the target signal from precipitation is the component in the orthogonal channel because the sense of the circular polarization is reversed as its direction of propagation changes when it is scattered back toward the radar. 3. A ratio that describes the degree to which radar clutter is suppressed by a clutter filter. This usage applies particularly to moving-target indication (MTI) radars. Shrader and Gregers-Hansen recommend that the term “improvement factor” be used in place of “cancellation ratio” because the latter term has been used inconsistently. Compare circular depolarization ratio.
Industry:Weather
1. In cloud physics, an obsolete term denoting any process that converts the numerous small cloud drops into a smaller number of larger precipitation particles. When so used, the term is employed in analogy to the coagulation of any colloidal system. The process can take place at temperatures both above and below 0°C for supercooled drops. See coalescence. 2. Similar to accretion. 3. The process whereby aerosol or colloidal particles collide with each other by Brownian motion and coalesce (liquid) or aggregate (solid).
Industry:Weather
1. Any process or sequence of states in which the initial and final states of a system are the same. 2. A unit of wave frequency, actually one cycle per second. See kilocycle, megacycle, kilomegacycle.
Industry:Weather
1. Any one of the semi-permanent highs and lows that appear on mean charts of sea level pressure. As originally used by L. Teissenenc de Bort in 1881, this term was applied to maxima and minima of pressure on daily charts. The main centers of action in the Northern Hemisphere are the Icelandic low, the Aleutian low, the Azores high and/or Bermuda high, the Pacific high, the Siberian high (in winter), and the Asiatic low (in summer). Other less intense or less consistent mean systems may be considered. Fluctuations in the nature of these centers are intimately associated with relatively widespread and long-term weather changes. 2. As used by Sir Gilbert Walker, any region in which the variation of any meteorological element is related to weather of the following season in other regions.
Industry:Weather
1. An organized unit of convection within a convecting layer. It is isolated by a stream surface, with ascending motion in the center and descending motion near the periphery, or vice versa. In laboratory convection, such cells (sometimes referred to as Bénard cells) are usually roughly as deep as they are wide, may take the form of squares, triangles, or hexagons, and may be laminar or turbulent and steady or oscillatory. In atmospheric boundary layer convection, this term refers to an organization of turbulent convection on horizontal scales at least as large as the depth of the convective boundary layer. In the case of cloud-topped boundary layers, convection cells may take the form of open cells, with broad, cloud-free areas of gentle descent surrounded by narrow updrafts within cumulus clouds, or may take the form of closed cells in stratocumulus clouds, characterized by narrow downdrafts at the periphery. See also cell, airmass thunderstorm, ordinary cell. 2. In the case of precipitating moist convection, refers to a distinct unit of convection, often having its own closed contours of radar reflectivity and a lifetime of roughly 20–30 minutes. Such a cell generally begins as a cumulus updraft, then develops a precipitation-driven downdraft, and finally decays as a general, cloudy area containing weak downdrafts.
Industry:Weather
1. Any movement of material in space. See air current, ocean current. 2. Any movement of electric charge in space, by virtue of which a net transport of charge occurs as, for example (in atmospheric electricity), in a conduction current, convection current, or precipitation current.
Industry:Weather
1. An influence that is relevant for determining the climate state in a region; much the same as climatic control, but regarded as including more local influences, such as the effects on the climate of local aerosol loading or extensive paving in or near a city. 2. An influence that has a major effect on human activities or human history. For example, it has been suggested that climate change may have been a factor in the disappearance of the Anasazi culture in the North American southwest.
Industry:Weather
1. An instability due to the buoyancy force of heavy fluid over light fluid overcoming the stabilizing influence of viscous forces. 2. Same as potential instability. 3. Same as thermal instability.
Industry:Weather
