- 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, ...
A hygrometer technically very similar to the Lyman-alpha hygrometer, but with the hydrogen radiation source replaced by a Krypton glow tube. The main emission is at 123. 58 nm, and the main advantages are a longer lifetime of the Krypton tube and a better calibration stability compared to the Lyman-alpha hygrometer, which makes this instrument more suitable for continuous humidity recordings. On the other hand, the sensitivity of the Krypton hygrometer is distinctly lower; therefore it is used mainly for ground- based measurements.
Industry:Weather
A hygrometer based on the absorption of radiation by water vapor at the Lyman-alpha line, which is an emission line of atomic hydrogen at 121. 567 nm. Lyman-alpha radiation can be generated by a glow discharge in hydrogen, and detection is normally accomplished by a nitric oxide ion chamber. Two magnesium fluoride windows both at the radiation source and the detector bound the absorption path. Lyman-alpha hygrometers are used on aircraft and on meteorological towers for high-frequency humidity measurements. Inconveniences of the method, like drift of the source intensity or contamination of the windows, are overcome by special calibration techniques or by baselining the high-frequency output to the humidity values provided by a slower, but stable, hygrometer.
Industry:Weather
A hot-wire type instrument for measuring the liquid water content of clouds in situ. The probe is most often used on research aircraft, but also occasionally at mountain-top installations and in wind tunnels. Resistivity changes, which occur as cloud droplets in the airflow that impinge on, and evaporate from, an exposed electrically heated wire, are sensed by an electric circuit. The liquid water content of the air is estimated from this signal using compensations for air temperature variations detected by a similar unexposed wire in the probe and knowledge of the airspeed.
Industry:Weather
A hot, dry, west or southwest wind of foehn type in the lee of the Sri Lanka hills during the southwest monsoon in June and July. It is well developed at Batticaloa on the east coast, where it is strong enough to overcome the sea breeze and bring maximum temperatures of nearly 38°C.
Industry:Weather
A grounded metallic conductor with its upper extremity extending above the structure that is to be protected from damage due to lightning. The upper extremity, called the air terminal, should be raised well above the top of the structure, to yield an adequate radius of protection. The path to ground must consist of a conductor of low total resistance and must contain no points of high local resistance. Lower ends should be buried deeply enough in the earth that they will always be in good contact with soil moisture. Connection to water pipes usually affords a good ground. Compare lightning arrester.
Industry:Weather
A glacier experiencing glacier flow. Expansion or retreat is determined by the balance between mass accretion and mass depletion processes.
Industry:Weather
A general term for what is often called a sun pillar, but one that allows for its appearance with such things as street lamps.
Industry:Weather
A fundamental radiation law that equates the absorptivity of matter to its emissivity at the same wavelength. Loosely put, this important law asserts that good absorbers of radiation at a given wavelength are also good emitters at that wavelength. For Kirchhoff's law to hold, the matter must be in local thermodynamic equilibrium, but the law is otherwise quite general, and applies to both natural and idealized surfaces or volumes. For natural surfaces it is often necessary to make the absorptivities and emissivities functions of direction and polarization state before applying the law.
Industry:Weather
A front (usually a cold front) at which the warm air descends the frontal surface (except, presumably, in the lowest layers). Compare anafront.
Industry:Weather
