- 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, ...
A measure of the diameter that contributes most to cloud liquid water or mass. See drop-size distribution.
Industry:Weather
One of several measures of central tendency. 1) Pertaining to a series of numbers, the median is the middle term when the numbers are arranged in algebraic order. If the number of terms is even, the median is taken as halfway between the two middle terms. 2) Pertaining to a continuous random variable ''x'', the median is that value that divides the probability distribution into two equal areas. Hence, in terms of the distribution function ''F''(''x''), the median is that value of ''x'' for which ''F''(''x'') = 1/2. In case ''F''(''x'') is discontinuous, the median is defined in such a way as to yield consistent results when the area is cumulated from either end of the distribution.
Industry:Weather
Any mixing process that utilizes the kinetic energy of relative fluid motion. The archetype of mechanical mixing is the instability of a vertically sheared flow. Consider a flow with an upper and a lower layer flowing in opposite directions. If the flow is unstable, perturbations grow by transferring momentum (through Reynolds stresses) between the layers and reducing the velocity difference between them. The kinetic energy of the shear flow (proportional to the mean-square velocity) is therefore reduced, and the energy has gone into the perturbations. These perturbations grow to the point where they become turbulent and cause vertical mixing.
Industry:Weather
An internal boundary layer caused by advection of air across a discontinuity in surface roughness. When the new surface is rougher than the old one, the MIBL depth grows roughly as the 0. 8 power of the ratio of the two roughness lengths. In this example, the MIBL grows to include the whole surface layer.
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
The process whereby solutes are mechanically mixed by velocity variations at the microscopic level during advective transport.
Industry:Weather
In radar, the four-dimensional space (volume × time) from which received target signals are sampled and processed to provide a measurement of reflectivity, the Doppler spectrum, or other properties of the target. Normally the measurement cell is large compared with the coherence element to provide an adequate average of the quantity to be measured or to reduce the amount of data to be stored.
Industry:Weather
After U. S. Weather observing practice, the ceiling classification that is applied when the ceiling value has been determined by means of 1) a ceiling light or ceilometer, provided that penetration of the beam is not in excess of that normally experienced for the height and type of layer and that the elevation angle indicated by the clinometer or ceilometer detector does not exceed 84°; 2) the timed disappearance of a radiosonde balloon with its height computed; 3) the known heights of unobscured portions of objects, other than natural landmarks, within 1½ nautical miles of any runway of the airport. A measured ceiling pertains only to clouds or to obscuring phenomena aloft. It is designated M in aviation weather observations.
Industry:Weather
The mean square of any residual. In case the mean residual is zero, the mean-square error is the same as the residual variance. See regression.
Industry:Weather
Dispersion of smoke plumes in the horizontal by means of the crosswind component (fluctuations) of the horizontal wind speed. The result is a plume that wanders from side to side. When averaged over a finite time period, the result is plume spreading in the horizontal.
Industry:Weather
