- 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, ...
An approximate law of scattering of electromagnetic waves by molecules and particles small compared with the wavelength of the illumination at wavelengths for which absorption is sufficiently small. According to this law, first derived in 1871 by Lord Rayleigh using simple dimensional arguments, scattering in all directions by an object is inversely proportional to the fourth power of the wavelength of the illumination. Scattering of sunlight by air molecules does not obey this law exactly, although it is a good approximation. Rayleigh's scattering law also predicts that scattering by a particle is proportional to the square of its volume. Compare Mie theory.
Industry:Weather
In radar meteorology, a sampling problem that arises when echoes located beyond the maximum unambiguous range (''r''<sub>max</sub>) are received as if they were within this range of the radar. A radar ordinarily computes range to targets by measuring the time interval between the transmission of a pulse and the receipt of the returned signal, assuming that the signal was associated with the pulse just transmitted. However, depending on the pulse repetition frequency, the returned signal may be associated with one of several pulses transmitted prior to the latest one. Therefore, a returned signal, indicated as originating at range ''r'', could have originated at ''r'' + ''r''<sub>max</sub> (second-trip echo), or ''r'' + 2''r''<sub>max</sub> (third-trip echo), etc. A range-aliased echo from a weather target is sometimes recognizable by a distorted shape. It may appear elongated radially or shrunk in azimuth extent because the radial length is unaffected by aliasing and is a correct measure of the target size while the azimuthal width decreases with increasing range from the radar.
Industry:Weather
In radar meteorology, a sampling problem that arises when echoes located beyond the maximum unambiguous range (''r''<sub>max</sub>) are received as if they were within this range of the radar. A radar ordinarily computes range to targets by measuring the time interval between the transmission of a pulse and the receipt of the returned signal, assuming that the signal was associated with the pulse just transmitted. However, depending on the pulse repetition frequency, the returned signal may be associated with one of several pulses transmitted prior to the latest one. Therefore, a returned signal, indicated as originating at range ''r'', could have originated at ''r'' + ''r''<sub>max</sub> (second-trip echo), or ''r'' + 2''r''<sub>max</sub> (third-trip echo), etc. A range-aliased echo from a weather target is sometimes recognizable by a distorted shape. It may appear elongated radially or shrunk in azimuth extent because the radial length is unaffected by aliasing and is a correct measure of the target size while the azimuthal width decreases with increasing range from the radar.
Industry:Weather
A cone-tipped metal rod designed to be driven downward into deposited snow or firn. The measured amount of force required to drive the rod a given distance is an indication of the physical properties of the snow or firn.
Industry:Weather
A ground-based, steerable radio antenna that tracks a moving radiotransmitter such as that contained in a radiosonde. See radio direction finding.
Industry:Weather
An instrument that measures the rate at which rain is falling. In the Jardi design, water from the rain collector enters a chamber containing a float with a tapered needle that controls the rate of outflow. The higher the rain rate, the higher the float, and the greater the outflow.
Industry:Weather
Rainfall that is retained in a basin during a storm event and does not contribute to direct runoff. Retention occurs due to the processes of infiltration, interception, and depression storage.
Industry:Weather
An onboard radar for determining the altitude of an aircraft above an underlying surface. Pulse-radar techniques measure altitude in terms of the transit time of the radar pulse; continuous-wave radar measures altitude in terms of the phase difference between the transmitted and received signals.
Industry:Weather
A ground-based, steerable radio antenna that tracks a moving radiotransmitter such as that contained in a radiosonde. See radio direction finding.
Industry:Weather
A chart indicating the change in atmospheric pressure of a constant-height surface over some specified interval of time; comparable to a height-change chart. See pressure tendency, isallobar, differential chart.
Industry:Weather
