- 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, ...
Organized vertical motion on a larger scale than atmospheric free convection associated with cumulus clouds. The patterns of vertical motion in hurricanes or in migratory cyclones are examples of such convection.
Industry:Weather
Ocean surface waves that are nearly two-dimensional, in that the crests appear very long in comparison with the wavelength, and the energy propagation is concentrated in a narrow band around the mean wave direction.
Industry:Weather
Often synonymous with visible radiation but sometimes applied to electromagnetic radiation well outside the visible spectrum.
Industry:Weather
Local name for a strong southeast wind in the vicinity of Palmer in the Matanuska Valley of Alaska. The knik wind blows most frequently in the winter, although it may occur at any time of year. In winter the knik winds are accompanied by very pronounced temperature rises; cases of more than 10°C in 24 hours have been observed. These winds may last from one to ten days. They result from a pressure gradient normal to the Chugach Mountains, causing a pronounced foehn effect in the Matanuska Valley.
Industry:Weather
Localized, convective snow bands that occur in the lee of lakes when relatively cold airflows over warm water. In the United States this phenomenon is most noted along the south and east shores of the Great Lakes during arctic cold-air outbreaks.
Industry:Weather
Lightning is a transient, high-current electric discharge with pathlengths measured in kilometers. The most common source of lightning is the electric charge separated in ordinary thunderstorm clouds (cumulonimbus). Well over half of all lightning discharges occur within the thunderstorm cloud and are called intracloud discharges. The usual cloud-to-ground lightning (sometimes called streak lightning or forked lightning) has been studied more extensively than other lightning forms because of its practical interest (i.e., as a cause of injury and death, disturbances in power and communication systems, and ignition of forest fires) and because lightning channels below cloud level are more easily photographed and studied with optical instruments. Cloud-to- cloud and cloud-to-air discharges are less common than intracloud or cloud-to-ground lightning. All discharges other than cloud-to-ground are often lumped together and called cloud discharges. Lightning is a self-propagating and electrodeless atmospheric discharge that, through the induction process, transfers the electrical energy of an electrified cloud into electrical charges and current in its ionized and thus conducting channel. Positive and negative leaders are essential components of the lightning. Only when a leader reaches the ground does the ground potential wave (return stroke) affect the lightning process. Natural lightning starts as a bidirectional leader, although at different stages of the process unidirectional leader development can occur. Artificially triggered lightning starts on a tall structure or from a rocket with a trailing wire. Most of the lightning energy goes into heat, with smaller amounts transformed into sonic energy (thunder), radiation, and light. Lightning, in its various forms, is known by many common names, such as streak lightning, forked lightning, sheet lightning, and heat lightning, and by the less common air discharge; also, the rare and mysterious ball lightning and rocket lightning. An important effect of worldwide lightning activity is the net transfer of negative charge from the atmosphere to the earth. This fact is of great important in one problem of atmospheric electricity, the question of the source of the supply current. Existing evidence suggests that lightning discharges occurring sporadically at all times in various parts of the earth, perhaps 100 per second, may be the principal source of negative charge that maintains the earth–ionosphere potential difference of several hundred thousand volts in spite of the steady transfer of charge produced by the air–earth current. However, there also is evidence that point discharge currents may contribute to this more significantly than lightning. See also cloud-to-ground flash, intracloud flash lightning discharge.
Industry:Weather
Liquid moisture on exposed leaf surfaces or other exposed plant parts.
Industry:Weather
Italian name for a southwest wind; used especially in northern Corsica for the west or southwest wind that blows throughout the year, and especially in winter when it is often stormy. On windward slopes it brings rain, with thunderstorms in summer and autumn. After crossing the mountains it is warm and dry, but may be very turbulent.
Industry:Weather
Length scale of turbulent motion below which the effects of molecular viscosity are nonnegligible. In three-dimensional turbulence, the Kolmogorov scale is (ν2/ε)1/4, in which ν is the kinematic viscosity and ε is the energy dissipation rate per unit mass.
Industry:Weather
