- 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, ...
Indicating or having equal frequency or intensity of thunderstorm activity. See isoceraunic line, isobront.
Industry:Weather
After U. S. Weather observing practice, the ceiling classification applied when the reported ceiling value represents the vertical visibility upward into surface-based atmospheric phenomena (except precipitation). Such phenomena include fog, blowing snow, and all of the lithometeors. All indefinite ceilings are estimations, but one of the following must be used as a guide: 1) the distance an observer can see vertically into the obstruction; 2) the height corresponding to the top of a ceiling-light beam; 3) the height at which a ceiling balloon completely disappears; 4) the height determined by the sensor algorithm at automated stations. The letters “VV” (vertical visibility) are used to designate an indefinite ceiling.
Industry:Weather
A dry, dust-bearing wind from the northeast or east that blows in West Africa especially from late November until mid-March. It originates in the Sahara as a desert wind and extends southward to about 5°N in January and 18°N in July. It is associated with the high pressure area that lies over the northwest Sahara in winter and the adjoining part of the Atlantic in other seasons. In summer the cooler onshore southwest monsoon undercuts it, but the harmattan continues to blow at a height of about 2 km (3000–6000 ft) and sometimes deposits dust on ships at sea. This conflict of winds causes the so-called West African tornadoes. See doctor.
Industry:Weather
Counter- rotating horizontal vortices that commonly occur within the convective boundary layer; their major axes are aligned with the mean boundary layer wind-shear vector. The depth of the roll circulations is consistent with the depth of the boundary layer; the wavelength, measured from updraft to updraft in the cross-roll direction, is about three times the boundary layer depth.
Industry:Weather
Prolonged period of below-normal precipitation, causing deficiencies in water supply, as measured by below-normal streamflow, lake and reservoir levels, groundwater levels, and depleted soil moisture content.
Industry:Weather
Prolonged period of below-normal precipitation, causing deficiencies in water supply, as measured by below-normal streamflow, lake and reservoir levels, groundwater levels, and depleted soil moisture content.
Industry:Weather
An approximate geometrical procedure for determining the propagation of electromagnetic (and other) waves. According to this construction, every point of a wave front in a medium at any instant is the source of secondary spherical wavelets propagating with the phase velocity of the medium. The envelope of all these wavelets then determines the wave front at a later instant. This construction is approximate if for no other reason than that often the complicated electromagnetic fields in matter are not simple waves with well-defined fronts. Moreover, the Huygens construction in its original form requires an ad hoc obliquity factor in order to obliterate that part of the complete envelope that is not observed. This construction deflects attention from physical explanations of the propagation of electromagnetic waves: Only (charged) matter is the source of such waves, not wave fronts. Huygens's construction is sometimes useful in obtaining approximate mathematical solutions to some problems in wave propagation, but for many problems (e.g., scattering of a plane electromagnetic wave by an arbitrary sphere) this construction is useless.
Industry:Weather
An approximate geometrical procedure for determining the propagation of electromagnetic (and other) waves. According to this construction, every point of a wave front in a medium at any instant is the source of secondary spherical wavelets propagating with the phase velocity of the medium. The envelope of all these wavelets then determines the wave front at a later instant. This construction is approximate if for no other reason than that often the complicated electromagnetic fields in matter are not simple waves with well-defined fronts. Moreover, the Huygens construction in its original form requires an ad hoc obliquity factor in order to obliterate that part of the complete envelope that is not observed. This construction deflects attention from physical explanations of the propagation of electromagnetic waves: Only (charged) matter is the source of such waves, not wave fronts. Huygens's construction is sometimes useful in obtaining approximate mathematical solutions to some problems in wave propagation, but for many problems (e.g., scattering of a plane electromagnetic wave by an arbitrary sphere) this construction is useless.
Industry:Weather
A storm characterized by a fall of freezing liquid precipitation. The attendant formation of glaze on terrestrial objects creates many hazards.
Industry:Weather
