- 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 radio frequency electromagnetic radiation originating, principally, in the irregular surges of charge in thunderstorm lightning discharges. Atmospherics are heard as a quasi-steady background of crackling noise (static) on certain radio frequencies, such as those used to broadcast AM radio signals. Since any acceleration of electric charge leads to emission of electromagnetic radiation, and since the several processes involved in propagation of lightning lead to very large charge accelerations, the lightning channel acts like a huge transmitter, sending out radiation with frequencies of the order of 10 kHz. Atmospherics may occasionally be detected at distances in excess of 3500 km (2000 mi) from their source. Advantage has been taken of this characteristic by using radio direction-finding equipment to plot cloud-to-ground lightning locations, and to locate active thunderstorm areas in remote regions and in-between weather reporting stations.
Industry:Weather
A range of wavelengths over which there is relatively little absorption of radiation by atmospheric gases. The major windows are the visible window, from ∼0. 3 to ∼0. 9 μm; the infrared window, from ∼8 to ∼13 μm; and the microwave window, at wavelengths longer than ∼1 mm. The infrared window loses much of its transparency under very humid conditions due to continuum absorption by water vapor, and can become completely opaque when clouds are present.
Industry:Weather
Generally, any pattern with some roughly identifiable periodicity in time and/ or space. In atmospheric dynamics, waves may be of acoustic, gravity, or Rossby type.
Industry:Weather
The requirement that the change in the amount of water stored in the atmosphere moving across a region should equal the difference between precipitation input to and evaporation loss from the underlying surface.
Industry:Weather
The movement of chemical species through the atmosphere as a result of large-scale atmospheric motions. The motions can be localized, such as convective systems, or synoptic in nature.
Industry:Weather
Defined in analogy to the oceanic tide as an atmospheric motion of the scale of the earth, in which vertical accelerations are neglected (but compressibility is taken into account). Both the sun and moon produce atmospheric tides, and there exist both gravitational tides and thermal tides. The harmonic component of greatest amplitude, the 12-hour or semidiurnal solar atmospheric tide, is both gravitational and thermal in origin, the fact that it is greater than the corresponding lunar atmospheric tide being ascribed usually to a resonance in the atmosphere with a free period very close to the tidal period. Other tides of 6, 8, 12, and 24 hours have been observed.
Industry:Weather
The study of thermodynamics as applied to atmospheres. Specification to the earth's atmosphere limits the important ranges of temperature, pressure, and gaseous components, but demands emphasis on the effects of phase changes of water.
Industry:Weather
The comprehensive study of the physics, chemistry, and dynamics of the earth's atmosphere, from the earth's surface to several hundred kilometers; this usually includes atmospheric chemistry, aeronomy, magnetospheric physics, and solar influences on the entire region.
Industry:Weather
Measurements, from the ground, an airborne platform, or a satellite, of atmospheric parameters (such as temperature or water vapor) at various heights or pressure levels.
Industry:Weather
Any one of a number of strata or “layers” of the earth's atmosphere. Temperature distribution is the most common criterion used for denoting the various shells. The troposphere (the “region of change”) is the lowest 10 or 20 km of the atmosphere, characterized by decreasing temperature with height. The term stratosphere is used to denote both 1) the relatively isothermal region immediately above the tropopause, and 2) the shell extending upward from the tropopause to the minimum temperature level at 70–80 km; the mesosphere is the shell between about 20 and 70 or 80 km that has a broad maximum temperature at about 40 or 50 km; and the thermosphere is the shell above the mesosphere with a more or less steadily increasing temperature with height. The distribution of various physico-chemical processes is another criterion. The ozonosphere, lying roughly between 10 and 50 km, is the general region of the upper atmosphere in which there is an appreciable ozone concentration and in which ozone plays an important part in the radiative balance of the atmosphere. The ionosphere, starting at about 70 or 80 km, is the region in which ionization of one or more of the atmospheric constituents is significant. The neutrosphere, the shell below this, is, by contrast, relatively un-ionized. The chemosphere, with no very definite height limits, is the region in which photochemical reactions take place. Dynamic and kinetic processes are a third criterion. The exosphere is the region at the “top” of the atmosphere, above the critical level of escape, in which atmospheric particles can move in free orbits, subject only to the earth's gravitation. Composition is a fourth criterion. The homosphere is the shell in which there is so little photo-dissociation or gravitational separation that the mean molecular weight of the atmosphere is sensibly constant; the heterosphere is the region above this, where the atmospheric composition and mean molecular weight is not constant. The boundary between the two is probably at the level at which molecular oxygen begins to be dissociated, and this occurs in the vicinity of 80 or 90 km. For further subdivisions, see ionosphere, troposphere.
Industry:Weather
