- 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, ...
1. The vector average wind velocity at a point relative to the earth. 2. For the purpose of upper air reports from aircraft, mean wind is derived from the drift of the aircraft when flying from one fixed point to another or obtained by flying on a circuit around a fixed observed point and an immediate wind deduced from the drift of the aircraft.
Industry:Weather
The arithmetic mean of mean high water and mean low water. This level is not identical with mean sea level because of higher harmonics in the tidal constituents.
Industry:Weather
The average temperature of the air as indicated by a properly exposed thermometer during a given time period, usually a day, a month, or a year. For climatological tables, the mean temperature is generally calculated for each month and for the year. For charts, the observed mean values at station level are reduced to sea level by adding a correction for elevation, usually taken as 0. 5°C for each 100 m (1°F for 360 ft), but in some mountainous countries different rates are used, based on local observations. See true mean temperature.
Industry:Weather
The uniform depth to which the water would cover the earth if the solid surface were smoothed off and were parallel to the surface of the geoid. This depth would be about 2440 m.
Industry:Weather
The average time during which anything can be said to reside within a specified region or to exist unchanged; for example, the mean life of a chemical species in the atmosphere, the mean life of a radioactive nucleus, the mean life of photons in a cloud. For processes following the same exponential law as radioactive decay, mean life is related simply to half-life.
Industry:Weather
The interval of time between two successive meridional transits of the “mean sun,” an imaginary point moving with such constant angular velocity along the celestial equator as to complete one annual circuit in a time period exactly equal to that of the apparent (true) sun in its annual circuit. The mean solar day is 86 400 seconds, or 1. 0027379 sidereal day. This modification of the apparent solar day was devised as a means of smoothing the irregularities observed in apparent relative motion of sun and earth; the equation of time defines the difference between the two. Outside astronomical circles, the mean solar day is the day in common use, but since it is reckoned from noon to noon, it has been modified to the civil day for practical use.
Industry:Weather
Changes of mean sea level at a site over long periods of time, typically decades, also called secular changes. Global changes due to the increased volume of ocean water are called eustatic changes; vertical land movements of regional extent are called eperiogenic changes.
Industry:Weather
The arithmetic mean of hourly heights observed over some specified period. In the United States, mean sea level is defined as the mean height of the surface of the sea for all stages of the tide over a 19-year period. Selected values of mean sea level serve as the sea level datum for all elevation surveys in the United States. In meteorology, mean sea level is used as the reference surface for all altitudes in upper-atmospheric work; in aviation it is the level above which altitude is measured by a pressure altimeter. Along with mean high water, mean low water, and mean lower low water, mean sea level is a type of tidal datum. Compare half-tide level, still-water level.
Industry:Weather
Mean of the monthly minimum observed during a specific calendar month over a specific period of years.
Industry:Weather
Mean of the monthly maximum temperatures observed during a specific calendar month over a specific period of years.
Industry:Weather
