- 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 dimensionless combination of several physical variables (e.g., velocity, density, viscosity), usually with a physical interpretation. Dimensionless groups arise naturally in the scale analysis of equations. The sixth edition of the McGraw–Hill Encyclopedia of Science and Technology lists 12 pages of dimensionless groups. See Boussinesq number, Cauchy number, Grashoff number, Mach number, Nusselt number, Péclet number, Prandtl number, Rayleigh number, Richardson number, Rossby number, Strouhal number, Taylor number; see also dimensional analysis, similarity theory, Buckingham Pi theory.
Industry:Weather
An algorithm operating upon a sequence of discrete-time sampled data, designed to pass signals with selected temporal or spatial frequencies while attenuating signals with other temporal or spatial frequencies. Such filters are often used to pass desired signals while suppressing noise or interfering signals. Common types are low-pass filters, which suppress high-frequency energy; high-pass filters, which reject low-frequency energy; and bandpass filters, which reject low- and high-frequency energy, and pass only a limited range of frequencies in between.
Industry:Weather
The steady state resulting from the diffusion process, also known as gravitational equilibrium. In such a state the constituent gases of the atmosphere would be distributed independently of each other, the heavier decreasing more rapidly with height than the lighter. However, the occurrence of turbulent mixing precludes establishment of diffusive equilibrium. See isothermal equilibrium.
Industry:Weather
A form of double-diffusive convection that occurs when cold freshwater overlies warm salty water. If a parcel of warm and salty water is moved upward in the water column, it loses heat more quickly than it loses salt, becoming colder and saltier, and thus denser, than its environs, or than the water at its initial position. It then sinks beyond its initial position into water that is saltier but warmer. It then gains heat from this water and begins to rise past its initial position. Diffusive convection transports heat more efficiently than salt and is believed to be responsible for staircase- like structures observed in the arctic thermocline. See also double diffusive convection, Turner angle.
Industry:Weather
A technique for stripping a certain molecule or class of molecules from an airstream. The molecules of interest diffuse to the walls of a flow-through reactor, and are deposited there, while particulate matter passes through the reactor unchanged. The reactors are usually cylindrical or annular tubes, to maximize the surface area for a given volume, and the inner walls can be coated with chemicals to remove the molecules of interest, for example, citric or oxalic acid for ammonia removal. At the end of a given time the chemicals of interest are removed from inside the denuder for quantitative chemical analysis.
Industry:Weather
1. The relative mean molecular velocity of a selected gas undergoing diffusion in a gaseous atmosphere, commonly taken as a nitrogen (N2) atmosphere. The diffusion velocity is a molecular phenomenon and depends upon the gaseous concentration as well as upon the pressure and temperature gradients present. 2. The speed with which a turbulent diffusion process proceeds as evidenced by the motion of individual eddies.
Industry:Weather
A set of mathematical equations that simulates the diffusion of material released in the atmosphere (or ocean). Usually in the form of computer codes, diffusion models simulate diffusion in a variety of physical processes.
Industry:Weather
A hygrometer based upon the diffusion of water vapor through a porous membrane. In its simplest form, it consists of a closed chamber having porous walls and containing a hygroscopic compound. The absorption of water vapor by the hygroscopic compound causes a pressure drop within the chamber that is measured by a manometer.
Industry:Weather
Solar radiation that is scattered at least once before it reaches the surface. As a percentage of the global radiation, diffuse radiation is a minimum, less than 10% of the total, under clear sky conditions and overhead sun. The percentage rises with increasing solar zenith angle and reaches 100% for twilight, overcast, or highly turbid conditions. It is measured by a shadow band pyranometer.
Industry:Weather
