- Industry: Weather
- Number of terms: 60695
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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, ...
An area of low atmospheric pressure near the surface resulting from heating of the lower troposphere and the subsequent lifting of isobaric surfaces and divergence of air aloft. Thermal lows are common to the continental subtropics in summer; they remain stationary over the warm surface areas that produce them; their cyclonic circulation is generally weak and diffuse; they are nonfrontal. Compare monsoon low.
Industry:Weather
Closed isotherms indicating an area of the surface that is relatively warm; most commonly associated areas of human disturbance such as towns and cities. The physiographic analogy derives from the similarity between the pattern of isotherms and height contours of an island on a topographic map. Heat islands commonly also possess “cliffs” at the urban–rural fringe and a “peak” in the most built-up core of the city. The annual mean temperature of a large city (say 10<sup>6</sup> inhabitants) may be 1°–2°C warmer than before development, and on individual calm, clear nights may be up to 12°C warmer. The warmth extends vertically to form an urban heat dome in near calm, and an urban heat plume in more windy conditions.
Industry:Weather
Diffusion or dispersion due to the effects of turbulent motions. When quantifying turbulent diffusion, it is important to distinguish between two types of measurement: 1) single-particle diffusion, where we measure the distances between diffusing particles at a fixed point or a point moving with the mean fluid velocity, and where the mean-square particle displacement initially increases rapidly with time (e.g., linearly); and 2) two-particle diffusion, where we measure the distances between particle pairs or the dimensions of a cloud of diffusing particles. Here the mean-square distance initially increases more slowly (e.g., as the 5/ 2 power of the time).
Industry:Weather
The distance, under daylight conditions, at which the apparent contrast between a specified type of target and its background becomes just equal to the threshold contrast of an observer; to be distinguished from the night visual range. The visual range is a function of the atmospheric extinction coefficient, the albedo and visual angle of the target, and the observer's threshold contrast at the moment of observation. Only in the so-called meteorological range does one have a visibility figure dependent only upon the extinction coefficient. See visual-range formula; Compare visibility.
Industry:Weather
The distance, under daylight conditions, at which the apparent contrast between a specified type of target and its background becomes just equal to the threshold contrast of an observer; to be distinguished from the night visual range. The visual range is a function of the atmospheric extinction coefficient, the albedo and visual angle of the target, and the observer's threshold contrast at the moment of observation. Only in the so-called meteorological range does one have a visibility figure dependent only upon the extinction coefficient. See visual-range formula; Compare visibility.
Industry:Weather
A type of directional antenna comprising an elevated linear array of horizontal dipoles with different lengths and spacings, typically arranged as a driven element, reflector element, and several director elements. The dipoles are organized to maximize the radiation in the forward direction. Radar systems requiring large antennas often use arrays of Yagi-Uda antennas (e.g., some wind profiler radars).
Industry:Weather
A severe tropical cyclone in the western North Pacific. The name is derived either from Cantonese t'ai fung (a “great wind”), from Arabic tufan (“smoke”), or from Greek typhon (a “monster”). Aristotle used typhon for a wind-containing cloud (''Meteorologica'', III, 1). For a more complete discussion, see tropical cyclone.
Industry:Weather
Gauging station at which two water level gauges are used to define the water surface slope for developing a stage–discharge relationship.
Industry:Weather
