- 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, ...
The commonly used abbreviation for instrument flight rules; in popular aviation terminology, descriptive of the conditions of reduced visibility to which instrument flight rules apply. Compare VFR.
Industry:Weather
The climatological position of the extreme minimum or maximum of sea ice extent.
Industry:Weather
The climate of the historical period, which may be taken as the past 7000 years; generally distinguished from the period of time during which regular daily observations from meteorological instruments are available, which begins generally in the seventeenth to eighteenth centuries A. D. Thus, historical climate is the climate of a period of history for which no instrumental observations exist, but its main characteristics may be reconstructed from written descriptions.
Industry:Weather
The average time interval under specified atmospheric conditions between the formation and destruction of an ion of any given type. The mean life of small ions in clean air, for example, over the sea, is four to five minutes, but in polluted air it is generally less than a minute. Large ions have mean lifetimes of as much as 15 to 20 minutes over the oceans, while in very polluted areas, lifetimes may approach an hour.
Industry:Weather
The belts of latitude over the oceans at approximately 30°–35°N and S where winds are predominantly calm or very light and weather is hot and dry. These latitudes mark the normal axis of the subtropical highs, and move north and south by about 5° following the sun. The two calm belts are known as the calms of Cancer and calms of Capricorn in the Northern and Southern Hemispheres, respectively; in the North Atlantic Ocean, these are the latitudes of the Sargasso Sea. The name is believed to have originated in the days of sailing ships, when the voyage across the Atlantic in those latitudes was often prolonged by calms or baffling winds so that water ran short, and ships carrying horses to the West Indies found it necessary to throw the horses overboard. Compare doldrums.
Industry:Weather
The audio-frequency signal transmitted by the Diamond–Hinman radiosonde when the baroswitch pen passes each fifteenth contact of the commutator, up to a number determined by the design of the commutator, and each fifth contact thereafter. This signal is transmitted so that the pressure, temperature, and humidity may be more readily distinguished.
Industry:Weather
The atmospheric region containing significant concentrations of ions and electrons. Its base is at about 70–80 km and it extends to an indefinite height. In terms of the standard upper-atmospheric nomenclature, the ionosphere is collocated with the thermosphere and the upper mesosphere, while the outer ionosphere also forms part of the magnetosphere. Most of the early knowledge of the ionosphere came from sounding by ground-based radars known as ionosondes, and the sharply defined echoes produced by these instruments led to the definition of ionospheric layers, implying well-defined regions with clear maxima of ionization. More recent investigations by a number of remote and in situ techniques have shown that such sharply bounded layers do not generally exist (with the exception of the so-called sporadic-E layers), and that the layers are better described as regions. The term layer is still frequently used, however. Ionospheric sounding normally shows an E-layer in the 100- to 120-km height range, an F1-layer in the 150- to 190-km range, and an F2-layer above 200 km. The D-region, lying in the upper mesosphere below 100 km, is responsible for daytime absorption of high-frequency radio waves, but does not usually produce an echo on ionosonde recordings. Early suggestions of a C-layer below the D-region, and a G-layer above the F2-layer, have not been generally accepted, and these terms are now obsolete. Over most of the earth, the ionosphere is produced by the action of solar radiation of short wavelength (extreme ultraviolet and x-ray radiation) on the atmospheric constituents. At high magnetic latitudes, energetic particles of solar or auroral origin become important, and even dominant, sources of ionization. See atmospheric shell.
Industry:Weather
The artificial application of water to land to promote the growth of crops. First practiced in arid lands to supplement deficient rainfall, it is now used extensively in more humid areas to ensure proper timing of water supply for maximum crop yield. The earliest form of irrigation consisted of diverting flood flows of streams onto the cropland. More common practice today is the storage of floodwaters in reservoirs from which the water may be withdrawn for use as needed. Extensive irrigation projects have been developed that use groundwater pumped from wells.
Industry:Weather
The assumption that the force of gravity is balanced by the vertical component of the atmospheric pressure gradient force, as must occur in the absence of atmospheric motions.
Industry:Weather
The arrangement of water molecules in an ice crystal. Under normal atmospheric temperatures and pressures between 0° and −100°C, water molecules arrange themselves into an hexagonal crystalline structure called ice-Ih. When viewed along the principal c axis these molecules form spatial hexagonal rings lying above each other, each water molecule surrounded by four others, in a near tetrahedral arrangement.
Industry:Weather
