- 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 character of the sunrise or sunset when the disk of the sun is hidden at these times by clouds or an obscuring phenomenon. Compare clear. 2. In popular usage, the state of the weather when clouds predominate at the expense of sunlight, or obscure the stars at night. In weather forecast terminology, expected cloud cover of about 0. 7 or more warrants the use of this term. Compare clear, partly cloudy.
Industry:Weather
1. Proposed intermediate in the ozonolysis of ethylene, formula CH2OO, formally a biradical species, which has two free radical sites. 2. Family of biradicals formed from the reaction of ozone with alkenes in the atmosphere. The yields of Criegee intermediates, and their subsequent reactions, are not fully characterized.
Industry:Weather
1. Same as climatic diagram. 2. (Rare. ) A coded numerical statement of the principal climatic elements of a location. See CLIMAT broadcast.
Industry:Weather
1. In weather radar, the shape of the beam produced by a typical parabolic antenna. The envelope of the main lobe, as defined by the half-power beamwidth, is a cone with the apex at the radar location. 2. In tracking radar, the beam produced by conical scanning methods.
Industry:Weather
1. In weather observations, the height of the cloud base above local terrain. Compare ceiling. 2. (Rare. ) The height of the cloud top above local terrain or above mean sea level. 3. (Rare. ) The vertical distance from the cloud base to the cloud top; more commonly referred to as the “thickness” or “depth” of the cloud.
Industry:Weather
1. In weather analysis and forecasting, a graphic representation of a vertical surface in the atmosphere, along a given horizontal line or path, and extending from the earth's surface to a given altitude. The type of data and analysis presented on such a cross-sectional chart depends upon its purpose. In meteorology, a synoptic cross section is prepared from synoptic weather data. In aviation, a flight cross section (or route cross section) is a graphic forecast of conditions expected to be encountered along the proposed flight route; therefore, time varies along the horizontal axis of the chart. Compare time section. 2. Generally, a two-dimensional, representative picture of a three-dimensional entity; usually a section or slice perpendicular to the principal axis of the entity, or passing through its center, or otherwise representative of a given aspect of the entity. See scattering cross section; compare profile, contour.
Industry:Weather
1. In oceanography, same as overturn. 2. In limnology, the process by which lake layers shift due to wind and temperature effects.
Industry:Weather
1. In tracking radar, a method of angular tracking in which the direction of the main lobe of the antenna pattern is slightly offset from the axis of the antenna. Rotation of the beam about the axis generates a cone with the antenna at the vertex and a vertex angle comparable in size to the beamwidth. Such an arrangement allows for accurate determination of the bearing and elevation of point targets, but is not used in weather radar. 2. In weather radar, the name sometimes applied to horizontal scanning because the surface swept in space by the beam as the antenna rotates in azimuth with fixed elevation angle is a cone.
Industry:Weather
1. In mathematics, a system of differential equations and supplementary conditions such that the values of all the unknowns (dependent variables) of the system are mathematically determined for all values of the independent variables (usually space and time) to which the system applies. 2. In thermodynamics, a system of fixed mass. By some definitions such a system may be confined to an impermeable container. An idealized air parcel, not diffusing into or mixing with its environment and undergoing a saturation- adiabatic process, is closed, as contrasted to one undergoing pseudoadiabatic expansion with precipitation removed. Compare open system, isolated system. 3. In synoptic meteorology, loosely used for a closed low or closed high.
Industry:Weather
1. In general, mass motions within a fluid resulting in transport and mixing of the properties of that fluid. Convection, along with conduction and radiation, is a principal means of energy transfer. Distinction is made between free convection (gravitational or buoyant convection), motion caused only by density differences within the fluid; and forced convection, motion induced by mechanical forces such as deflection by a large-scale surface irregularity, turbulent flow caused by friction at the boundary of a fluid, or motion caused by any applied pressure gradient. Free and forced convection are not necessarily exclusive processes. On a windy day with overcast sky, the heat exchange between ground and air is an example of forced convection. On a sunny day with a little wind where the ground temperature rises, both kinds of convection take place. 2. (Or gravitational or buoyant convection. ) Motions that are predominantly vertical and driven by buoyancy forces arising from static instability, with locally significant deviations from hydrostatic equilibrium. Atmospheric convection is nearly always turbulent. Convection may be dry, that is, with relative humidities less than 100%, especially in the boundary layer, but is commonly moist, with visible cumuliform clouds. Most convective clouds are driven by positive buoyancy, with virtual temperature greater than the environment, but clouds with precipitation, evaporation, and/or melting can produce negatively buoyant convection. See slantwise convection. 3. As specialized in atmospheric and ocean science, a class of relatively small-scale, thermally (can be driven by salt concentration in the ocean) direct circulations that result from the action of gravity upon an unstable vertical distribution of mass. (In the case of slantwise convection, though, the motions are larger scale, and are driven by a combination of gravitational and centrifugal forces acting at an angle to the vertical. )
Almost all atmospheric and oceanic convection is fully turbulent and is generally composed of a collection of convection cells, usually having widths comparable to the depth of the convecting layer. In the atmosphere, convection is the dominant vertical transport process in convective boundary layers, which are common over tropical oceans and, during sunny days, over continents. In the ocean, convection is prominent in regions of high heat loss to the atmosphere and is the main mechanism of deep water formation. Moist convection in the atmosphere is characterized by deep, saturated updrafts and downdrafts, and unsaturated downdrafts driven largely by the evaporation and melting of precipitation. This form of convection is made visible by cumulus clouds and, in the case of precipitating convection, by cumulonimbus clouds. Moist convection and radiation are the dominant modes of vertical heat transport in the Tropics. 4. In atmospheric electricity, a process of vertical charge transfer by transport of air containing a net space charge, or by motion of other media (e.g., rain) carrying net charge. Eddy diffusion of air containing a net charge gradient may also yield a convection current.
Industry:Weather
