- 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 sporadic radiant emission from the upper atmosphere over the middle and high latitudes. It is believed to be due primarily to the emission of the nitrogen molecule N2, its molecular ion N2+, and atomic oxygen (O). According to various theories, auroras seem definitely to be related to magnetic storms and the influx of charged particles from the sun. The exact details of the nature of the mechanisms involved are still being investigated. The aurora is most intense at times of magnetic storms (when it is also observed farthest equatorward) and shows a periodicity related to the sun's 27-day rotation period and the 11-year sunspot cycle. The distribution with height shows a pronounced maximum near 100 km. The lower limit is probably near 80 km. The aurora can often be clearly seen, and it assumes a variety of shapes and colors that are characteristic patterns of auroral emission. The names given to the various forms are 1) arcs, which are bands of light extending across the sky, the highest point of the arc being in the direction of the magnetic meridian; 2) rays, which may appear as single lines like a searchlight beam, or in bundles; 3) draperies, which have a curtainlike appearance, sharp on the bottom and tenuous in the upper parts; 4) crown or corona, which are seen when the rays appear to spread out from a single point in the sky; 5) bands, which are similar to the arcs, and may or may not have a ray structure; and 6) diffuse luminous surfaces, which appear as luminous clouds of indefinite shape. Sometimes the term “streamers” is used to describe the auroral forms that extend to great heights. In northern latitudes these displays are called aurora borealis, aurora polaris, or northern lights; in southern latitudes they are called aurora australis. Compare airglow.
Industry:Weather
A bright, faintly colored region of light surrounding the sun. The aureole is what a corona becomes when there is a broad range of droplet (or particle) sizes. Aureoles are fairly common. See solar aureole.
Industry:Weather
The ice formed when water from a spring or stream emerges and freezes on top of previously formed ice.
Industry:Weather
A region surrounding a sound source, such as an explosion, in which the sound can be detected, usually by a human without special aids. The concept of an audibility zone may be applied to frequencies outside the range of human hearing and to detectors far more sensitive than the human ear. The existence and geometry of audibility zones depend on temperature and wind component profiles along the the path between the source and the receiver. Audibility zones close to a source depend on the wind and temperature profiles in the boundary layer. At greater distances, temperature profiles in the stratosphere and mesosphere and the location of the tropospheric jet stream are the primary determinants of the location and extent of audibility zones.
Industry:Weather
A stable equilibrium state having the property that small departures from the equilibrium continually diminish. An attractor may be represented in a coordinate system as a single point (the usual case) or as a bounded set of infinitely many points (as in the case of a limit cycle). A strange attractor is an attractor containing an infinite number of points and having the property that small changes in neighboring states give rise to large and apparently unpredictable changes in the evolution of the system. The best-known example of a strange attractor in meteorology is that discovered by E. N. Lorenz (1963) in solutions to a simplified set of equations describing the motion of air in a horizontal layer heated from below.
Industry:Weather
1. (Also called extinction, especially in reference to optical frequencies. ) A general term used to denote a decrease in signal strength in transmission from one point to another. For the propagation of electromagnetic waves through a medium, attenuation is caused by absorption and scattering. The volume attenuation coefficient (m−1) of such a medium is the fractional reduction of radiance per unit pathlength. In radar usage, the specific attenuation is the fractional reduction in power density per unit pathlength as plane-wave radiation propagates through a medium, usually expressed in decibels per kilometer. Attenuation ordinarily does not refer to the inverse-square falloff of irradiance or power density with range that is simply a consequence of beam divergence. See extinction coefficient. 2. The scattering and absorption of radiant energy by clouds or the atmosphere that decreases the radiation received by satellite sensors.
Industry:Weather
In meteorological literature, often used with particular reference to the disappearance of free electrons by their attachment to neutral oxygen atoms or molecules, thus forming negative ions. The rate of the process is expressed by an attachment coefficient with dimensions of volume per time.
Industry:Weather
A thermometer that is attached to an instrument in order to determine its operating temperature. It is used whenever an instrument has a significant temperature coefficient, as in a mercury barometer.
Industry:Weather
Total number of protons (and hence electrons for a neutral atom) in an atomic nucleus.
Industry:Weather
