- 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, ...
Fog, light and of short duration, produced by the mixing of two moist but nonsaturated air masses with different temperatures.
Industry:Weather
A cloud formed when two subsaturated volumes of moist air with different temperatures and vapor pressures mix isobarically and adiabatically to form a volume of moist air with an intermediate temperature and vapor pressure above the saturation value at that temperature. Popular but misleading terms for mixing clouds are steam, steam fog, and steam clouds. These terms obscure the essential mechanism by which mixing clouds are formed and confuse water vapor with liquid water. Mixing clouds are the consequence of neither cooling nor heating because both volumes enter into the mixture symmetrically. They are a consequence of the nonlinearity of the Clausius–Clapeyron equation together with the linearity of the first law of thermodynamics for moist air. An example of a mixing cloud is a condensation trail.
Industry:Weather
1. The result of irregular fluctuations in fluid motions on all scales from the molecular to large eddies. Gradients of conservative properties such as potential temperature, momentum, humidity, and concentrations of particles and gaseous constituents are reduced by mixing, tending toward a state of uniform distribution. See turbulence, eddy flux, diffusion. 2. In electronics, the nonlinear (nonadditive) combining of signals. The common mixing element is a diode or set of diodes. The common desired result of mixing two sinusoidal signals is the multiplicative product, with terms at the sum and difference frequencies. Mixing is used to shift signals to different carrier frequencies.
Industry:Weather
Removal of pollutants out of the top of the atmospheric boundary layer through the mixed-layer capping inversion. Normally pollutants cannot escape through the capping inversion. However, penetrating cumulus clouds, thunderstorms, mountain circulations, and frontal circulations can force polluted air through the inversion to vent pollutants into the free atmosphere.
Industry:Weather
The thickness, ''z''<sub>i, </sub> of the mixed layer, defined as the location of a capping temperature inversion or statically stable layer of air. Often associated with, or measured by, a sharp increase of potential temperature with height, a sharp decrease of water-vapor mixing ratio, a sharp decrease in turbulence intensity, a sharp decrease in pollutant concentration, a change of wind speed to geostrophic, a minimum of turbulent heat flux, and a maximum of signal intensity from remote sensors such as sodars and wind profilers. Quite variable in space and time, the mixed-layer depth typically increases during fair-weather daytime over land from tens of meters shortly after sunrise to 1–4 km before sunset, depending on the location and season.
Industry:Weather
Fourier analysis spectra of velocity variance for the atmospheric mixed layer that exhibit universal similarity characteristics when properly normalized by mixed-layer scaling variables.
Industry:Weather
A tidal regime where both the diurnal and semidiurnal components are significant.
Industry:Weather
An eastward propagating equatorial wave that has a meridional velocity component symmetric about the equator and a zonal velocity component anti-symmetric about the MCC. For large positive (eastward) zonal wavenumbers its dispersion relation is Kelvin wave–like and for large but negative (westward) zonal wavenumbers its dispersion relation is Rossby wave– like. See also Rossby–gravity wave.
Industry:Weather
The statically stable layer of air at the top of the atmospheric boundary layer. Because the troposphere is statically stable on the average (i.e., potential temperature increases with height), and because turbulence in the boundary layer causes potential temperatures to become somewhat well mixed there, conservation of heat requires that there be a potential temperature increase (i.e., a temperature step or inversion) at the top of the boundary layer. It is this inversion that separates the boundary layer from the rest of the troposphere by limiting the domain of turbulence. It is also responsible for trapping pollutants near the ground during fair weather.
Industry:Weather
An approximation that treats the atmospheric boundary layer as though variables such as potential temperature, momentum, pollutants, and humidity were uniform with height. This type of model is popular because of its simplicity, requiring forecasts of only the average variables in the mixed layer and of the change of mixed-layer depth. During sunny days over land, the actual boundary layer is often sufficiently well mixed that a uniform slab approximation is a fairly good approximation.
Industry:Weather
