- 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, ...
Astronomically, between the summer solstice and autumnal equinox in the Northern Hemisphere, and beteen the winter solstice and vernal equinox in the Southern Hemisphere; the warmest season of the year everywhere except in some tropical regions. Popularly and for most meteorological purposes, summer is taken to include June, July, and August in the Northern Hemisphere, and December, January, and February in the Southern Hemisphere, the opposite of winter. See Indian summer, Old Wives' summer, St. Luke's summer, St. Martin's summer.
Industry:Weather
As originally coined in 1905 by Des Voeux: a natural fog contaminated by industrial pollutants, a mixture of smoke and fog. Today, it is the common term applied to problematical, largely urban, air pollution, with or without the natural fog; however, some visible manifestation is almost always implied. Smogs are constituted in great variety, but a major dichotomy exists between the photochemical smogs of nitrogen oxides and hydrocarbons emitted mainly by automobile engines and, on the other hand, the sulfur-laden, sometimes deadly, smogs produced by the large-scale combustion of fuel oil and coal. Both types contain carbon monoxide, carbon dioxide, and a variety of particulates. See Los Angeles (photochemical) smog, London (sulfurous) smog.
Industry:Weather
As defined by C. W. Thornthwaite in his 1948 climatic classification, a type of climate that has humidity index values of +100 and above. This is his wettest type of climate (letter code ''A'') and compares closely to the wet climate that heads his 1931 grouping of humidity provinces.
Industry:Weather
Aridity is a climatological condition in which the amount of precipitation received (supply) is exceeded, on average, by potential evapotranspiration (demand). A number of physically based indices have been proposed to describe this deficiency that relate precipitation to temperature and humidity. For practical purposes, in the temperate and tropical zones, semiarid climates generally receive between 200 and 500 mm of precipitation per year on average, and arid climates receive less than 200 mm. However, definitions based on mean precipitation are not always satisfactory, because they do not express variability or the likelihood of drought. Rainfall in arid climates is extremely variable, with coefficients of variation for arid climates exceeding 50%, and coefficients for semiarid climates ranging between 30% and 50%. In broad economic terms, variability restricts the potential use of these lands. Arid climates are unsuitable for growing crops using rainfall alone, because crops may fail three or more years out of ten. Semiarid climates often support grasses that are suitable for grazing animals. Thus, livestock raising is often more appropriate, less risky, and more common than rainfed agriculture in semiarid areas.
Industry:Weather
Areas of intensified brightness in the solar chromosphere that are usually observed in an emission line of calcium. These regions are usually broad and irregular and approximately coincide with faculae and sunspots in the underlying photosphere. The number and size of these regions varies during the solar cycle, causing enhanced chromospheric emission during solar maximum relative to a lower emission during solar minimum.
Industry:Weather
Approximate theory for electromagnetic scattering by small particles named for Lord Rayleigh (John William Strutt, 1842–1919), who in 1871 showed that the blue color of the clear sky is explained by the scattering of light by molecules in the atmosphere. The Rayleigh approximation to the more complex Mie theory requires that the particles be very small in comparison to the wavelength of the radiation. The range of applicability of the Rayleigh theory depends on the refractive index of the particles. For water drops the criterion is usually stated as ''D'' < λ/10, where ''D'' is the drop diameter and λ is the wavelength of the incident radiation. Characteristics of Rayleigh scattering are that the scattering cross section of a sphere of diameter ''D'' is proportional to ''D''<sup>6</sup>/λ<sup>4</sup> and that the phase function is proportional to (1 + cos<sup>2</sup>θ), where θ is the scattering angle. In radar, Rayleigh scattering theory is usually employed to interpret the observations of echoes from precipitation, even though the Rayleigh criterion is not satisfied by raindrops for wavelengths much shorter than 10 cm or by hailstones for even longer wavelengths. Corrections based on Mie theory are sometimes applied to observations at wavelengths shorter than 3 cm. Large raindrops and hailstones can deviate from spherical shape; radar scattering by nonspherical particles has been approximated by the Gans theory for small ellipsoids.
Industry:Weather
Applied to a physical quantity, especially a thermodynamic variable, usually means per unit mass. For example, specific volume is volume divided by mass, specific enthalpy is enthalpy divided by mass, and so on. Specific quantities are common in meteorology, and hence specific is often omitted as a qualifier, it being understood.
Industry:Weather
Any wind of lesser speed than the geostrophic wind required by the existing pressure gradient. A subgeostrophic wind is not necessarily a subgradient wind.
Industry:Weather
Any wind of greater speed than the geostrophic wind required by the existing pressure gradient. A supergeostrophic wind is not necessarily a supergradient wind.
Industry:Weather
