- 行业: 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, ...
In situ instruments that rapidly respond to turbulent fluctuations in atmospheric variables (e.g., velocity, temperature, and humidity). This capability typically requires a sensor time constant of < 1 s for tower-based sensors and in the range of 0. 01–0. 1 s for aircraft sensors.
Industry:Weather
In radar, a small region of locally high reflectivity from which a trail of hydrometeors originates. It is postulated that snow crystals are formed and grow in the generating cells and that the cells are maintained by convection induced by the release of latent heat accompanying the crystal growth. The shape of the snow trail below a generating cell depends on the fall speed of the snow and the vertical profile of the horizontal wind.
Industry:Weather
In radar, the strength of the electric field produced at a point by the transmitted radio waves, measured in microvolts or millivolts per meter.
Industry:Weather
In radiation, the radiant energy per unit time crossing a plane surface of unit area. Units are W m−2. See also irradiance, emittance.
Industry:Weather
In radar, a diffuse echo in the apparently clear air that is caused by a cloud of point targets such as insects or by Bragg scattering from spatial variations of the refractivity of truly clear air. Ghost echoes are incoherent echoes with characteristics similar to those of weather echoes. Compare angel; see clear-air echo.
Industry:Weather
In radar, a scattering mechanism proposed to explain certain kinds of clear- air echoes observed by UHF and VHF radars. Such echoes are observed by vertically pointing radars operating at wavelengths of about 1 m and longer. They are in the form of thin, horizontal layers that exhibit strong aspect sensitivity, in the sense that the reflectivity for a vertical beam is greater than that for off-vertical beams. They are thought to be explained by partial reflections from thin layers containing sharp vertical gradients of refractivity. The layers have vertical extents that are comparable to or less than a wavelength and horizontal extents that are as large as the width of the first Fresnel zone, namely, (zλ)½, where z is the altitude and λ is the radar wavelength. Echoes explained by Fresnel reflection have longer coherence times than those explained by Bragg scattering from beam-filling echoes and are more in the nature of specular reflections. Sometimes a distinction is made between Fresnel reflection and Fresnel scattering. The term scattering is used if there are several or many thin reflective layers in the pulse volume; reflection is reserved for the situation of only one layer in the pulse volume.
Industry:Weather
In nautical terminology, a contraction for “weather glass” (a mercury barometer).
Industry:Weather
