- 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, ...
The three-part change of the atmospheric boundary layer that typically occurs during fair weather over land on sunny days. In the early morning, the mixed layer is shallow, slowly deepening, cool (in a potential temperature sense), and is capped by the remains of the stable boundary layer from the previous night. In mid- to late morning, the top of the mixed layer exhibits rapid rise as heating eliminates the nocturnal inversion, and the mixed layer grows through the residual layer. The third stage in late morning and afternoon is that of a deep (order of 1–2 km) convective boundary layer of relatively constant depth.
Industry:Weather
A cloud condensation nucleus (CCN) composed of both soluble hygroscopic matter and insoluble, possibly wettable, matter. Its mixed composition probably results from a coagulation process or from cycles of condensation and evaporation, possibly involving chemical reactions. When applied to natural ice nuclei or cloud seeding nuclei (as silver iodide), the term implies the presence of a soluble component that leads to condensation prior to initiation of freezing.
Industry:Weather
A frequency distribution that is composed of a mixture of several unlike populations of data or populations with different parameters.
Industry:Weather
Models of the upper ocean (usually one-dimensional) that take advantage of the concept of a mixed layer by assuming 1) the mean temperature, salinity, and horizontal velocity are quasi-uniform within the mixed layer; and 2) a quasi-discontinuous distribution (jump) exists for the same variables just below the mixed layer. This permits integrating the momentum and tracer equations from the bottom of the mixed layer to the surface to get equations for the bulk mixed layer velocity, temperature, and salinity, and adding an equation for the evolution of the mixed-layer depth derived from the vertically integrated (across the mixed layer) turbulence kinetic energy (TKE) equation.
Industry:Weather
1. (Abbreviated ML; sometimes called convective mixed layer, convective boundary layer, or mixing layer in air-pollution meteorology. ) A type of atmospheric boundary layer characterized by vigorous turbulence tending to stir and uniformly mix, primarily in the vertical, quantities such as conservative tracer concentrations, potential temperature, and momentum or wind speed. Moisture is often not so well mixed, showing a slight decrease with height. The vigorous turbulence can be caused by either strong winds or wind shears that generate mechanical turbulence (called forced convection), or by buoyant turbulence (called free convection) associated with large thermals. The buoyantly generated mixed layers are usually statically unstable, caused by heating at the bottom boundary such as the earth's surface or radiative cooling at the tops of cloud or fog layers within the mixed layer. The terms mixed layer, convective mixed layer, and convective boundary layer commonly imply only the buoyantly stirred layer. During fair weather over land, mixed layers are usually daytime phenomena generated buoyantly, with growth caused by entrainment of free-atmosphere air into the mixed-layer top. See mixed-layer depth, entrainment zone, radix layer, uniform layer. 2. In oceanography, a fully turbulent region of quasi-isopycnal water (i.e., virtually uniform potential density) that, in the case of the surface mixed layer, is bounded above by the air-sea interface and below by the transition layer. Mixed layer depth is often defined as the depth at which potential density differs from that of the surface by 0. 01 kg m<sup>−1</sup>.
Industry:Weather
Environmental conditions favorable to promoting development of a vector (spores in the air or soil and insect populations) or disease.
Industry:Weather
A cloud containing both water drops (supercooled at temperatures below 0°C) and ice crystals, hence a cloud with a composition between that of a water cloud and that of an ice- crystal cloud. A mixed cloud is unstable in the sense that the equilibrium vapor pressure difference between water drops and ice crystals at subfreezing temperatures promotes growth of the ice crystals at the expense of the water drops, which is the basis for the Bergeron–Findeisen theory of precipitation. Most convective clouds extending into air colder than about −10°C are mixed clouds, though the proportion of ice crystals to water drops may be small until the cloud builds to levels of still lower temperature. Some clouds (lenticularis, mountain wave clouds) form at temperatures near −35°C and contain only very small amounts of ice crystals.
Industry:Weather
A frequency distribution that is composed of a mixture of several unlike populations of data or populations with different parameters.
Industry:Weather
A north wind that blows down the Rhone valley south of Valence, France, and into the Gulf of Lions. It is strong, squally, cold, and dry, the combined result of the basic circulation, a fall wind, and jet-effect wind. It blows from the north or northwest in the Rhône Delta, where it is strongest, from northwest in Provence and from northeast in the valley of the Durance below Sisteron. A general mistral usually begins with the development of a depression over the Tyrrhenian Sea or Gulf of Genoa with an anticyclone advancing from the Azores to central France. It often exceeds 27 m s<sup>−1</sup> (60 mph) and reaches 38 m s<sup>−1</sup> (85 mph) in the lower Rhône valley and 22 m s<sup>−1</sup> (50 mph) at Marseilles, decreasing both east and west and out to sea. It remains strong to a height of 2–3 km. In the absence of a strong pressure gradient, a weaker katabatic local mistral develops in the Rhône valley. A general mistral usually lasts for several days, sometimes with short lulls. It is most violent in winter and spring, and may do considerable damage. Market gardens and orchards are protected from it by windbreaks, and rural houses are built with only a few openings on the side exposed to it. The mistral has a variety of local names: mangofango in Provence; sécaire, maistrau, maistre, or magistral in Cévennes; dramundan in Perpignan; cierzo in Spain; cers in the Pyrenees, etc. South of Mont Ventoux a similar wind is named bise. A local west wind of mistral type that descends from Mt. Canigou to the plains of Roussillon is called canigonenc. Compare bora, tramontana, maestro; see also cavaliers.
Industry:Weather
An action to make something less severe. A mitigation plan for a source of pollutants is a plan to reduce the amount of pollutants emitted. A mitigation plan could be voluntary or in response to a regulation or law.
Industry:Weather
