- 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 virtual temperature ''T<sub>v</sub>'' = ''T''(1 + ''r<sub>v</sub>''/ ε)/(1 + ''r<sub>v</sub>''), where ''r<sub>v</sub>'' is the mixing ratio and ε is the ratio of the gas constants of air and water vapor, ≈ 0. 622. The virtual temperature allows the use of the dry-air equation of state for moist air, except with ''T'' replaced by ''T<sub>v</sub>''. Hence the virtual temperature is the temperature that dry dry air would have if its pressure and density were equal to those of a given sample of moist air. For typical observed values of ''r<sub>v</sub>'', the virtual temperature may be approximated by ''T<sub>v</sub>'' = (1 + 0. 61 ''r<sub>v</sub>'') ''T''. Some authors incorporate the density increment due to liquid or solid water into virtual temperature, in which case the definition becomes ''T<sub>v</sub>'' = ''T''(1 + ''r<sub>v</sub>''/ε)/(1 + ''r<sub>v</sub>'' + ''r<sub>l</sub>'') ≈ ''T''(1 + 0. 61''r<sub>v</sub>'' − ''r<sub>l</sub>''), where ''r<sub>l</sub>'' is the liquid or liquid plus solid water mixing ratio.
Industry:Weather
A wind that assists the intended progress of an exposed, moving object, for example, rendering an airborne object's groundspeed greater than its airspeed; the opposite of a headwind. The tailwind component is directed along the heading, not the course. See wind factor, crosswind.
Industry:Weather
Wisps or streaks of water or ice particles falling out of a cloud but evaporating before reaching the earth's surface as precipitation. Virga is frequently seen trailing from altocumulus and altostratus clouds, but also is discernible below the bases of high-level cumuliform clouds from which precipitation is falling into a dry subcloud layer. It typically exhibits a hooked form in which the streaks descend nearly vertically just under the precipitation source but appear to be almost horizontal at their lower extremities. Such curvature of virga can be produced simply by effects of strong vertical wind shear, but ordinarily it results from the fact that droplet or crystal evaporation decreases the particle terminal fall velocity near the ends of the streaks. Under some conditions, virga are associated with dry microbursts, which are formed as a product of the evaporation. See cloud classification.
Industry:Weather
A type of rain forest that exists in tropical regions where precipitation is heavy, generally more than 250 cm (98 in. ) per year. It consists mainly of a wide variety of lofty trees, which carry a profusion of parasitic or climbing plants, and, in some portions, a “jungle” of dense undergrowth near the ground. For lack of marked climatic seasons, growth proceeds throughout the year. Compare temperate rain forest.
Industry:Weather
The transport of any quantity ''S'' from small to large values, contrary to that expected by diffusion theory. Upgradient flux is typically observed in the top fifth of the atmospheric boundary layer, where heat flux is often observed to flow from colder to warmer values of potential temperature caused by nondiffusion transport processes such as convective thermals. Some theories that account for this countergradient flux include top-down/bottom-up diffusion and transilient turbulence theory.
Industry:Weather
The virtual temperature ''T<sub>v</sub>'' = ''T''(1 + ''r<sub>v</sub>''/ ε)/(1 + ''r<sub>v</sub>''), where ''r<sub>v</sub>'' is the mixing ratio and ε is the ratio of the gas constants of air and water vapor, ≈ 0. 622. The virtual temperature allows the use of the dry-air equation of state for moist air, except with ''T'' replaced by ''T<sub>v</sub>''. Hence the virtual temperature is the temperature that dry dry air would have if its pressure and density were equal to those of a given sample of moist air. For typical observed values of ''r<sub>v</sub>'', the virtual temperature may be approximated by ''T<sub>v</sub>'' = (1 + 0. 61 ''r<sub>v</sub>'') ''T''. Some authors incorporate the density increment due to liquid or solid water into virtual temperature, in which case the definition becomes ''T<sub>v</sub>'' = ''T''(1 + ''r<sub>v</sub>''/ε)/(1 + ''r<sub>v</sub>'' + ''r<sub>l</sub>'') ≈ ''T''(1 + 0. 61''r<sub>v</sub>'' − ''r<sub>l</sub>''), where ''r<sub>l</sub>'' is the liquid or liquid plus solid water mixing ratio.
Industry:Weather
An infrequently observed, faint white, circular arc or complete ring of light that has a radius of 39° and is centered on the antisolar point. When observed, it is usually in the form of a separate outer ring around an anticorona.
Industry:Weather
An infrequently observed, faint white, circular arc or complete ring of light that has a radius of 39° and is centered on the antisolar point. When observed, it is usually in the form of a separate outer ring around an anticorona.
Industry:Weather
The transport of any quantity ''S'' from small to large values, contrary to that expected by diffusion theory. Upgradient flux is typically observed in the top fifth of the atmospheric boundary layer, where heat flux is often observed to flow from colder to warmer values of potential temperature caused by nondiffusion transport processes such as convective thermals. Some theories that account for this countergradient flux include top-down/bottom-up diffusion and transilient turbulence theory.
Industry:Weather
Snow that, when melted, yields a greater-than-average amount of water; thus, any snow with a high water content.
Industry:Weather
