- 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 bottom layer of the troposphere that is in contact with the surface of the earth. It is often turbulent and is capped by a statically stable layer of air or temperature inversion. The ABL depth (i.e., the inversion height) is variable in time and space, ranging from tens of meters in strongly statically stable situations, to several kilometers in convective conditions over deserts. During fair weather over land, the ABL has a marked diurnal cycle. During daytime, a mixed layer of vigorous turbulence grows in depth, capped by a statically stable entrainment zone of intermittent turbulence. Near sunset, turbulence decays, leaving a residual layer in place of the mixed layer. During nighttime, the bottom of the residual layer is transformed into a statically stable boundary layer by contact with the radiatively cooled surface. Cumulus and stratocumulus clouds can form within the top portion of a humid ABL, while fog can form at the bottom of a stable boundary layer. The bottom 10% of the ABL is called the surface layer. Compare Ekman layer.
Industry:Weather
The reduction with distance from the source of the intensity of an acoustic or an electromagnetic signal propagating through the atmosphere caused by interaction of the signal with gaseous constituents of the atmosphere, aerosols, or hydrometeors. In general, scattering and absorption account for attenuation. For sound, absorption is usually more important than scattering; it depends on temperature and humidity, and generally increases with increasing acoustic frequency. The main atmospheric constituents that absorb radar energy are oxygen, water vapor, and liquid hydrometeors. Absorption is often neglected at wavelengths of 10 cm and longer, but becomes increasingly important at shorter wavelengths. The contribution of scattering to radar attenuation also increases with decreasing wavelength. For lidar, scattering by molecules, aerosols, and hydrometeors dominates the attenuation, although gaseous absorption is significant at certain spectral bands and is exploited by differential absorption lidar (DIAL) to measure molecular concentrations.
Industry:Weather
Interactions between the atmosphere and the ocean, as in air–sea interaction, but also including large spatial scale (up to global) effects.
Industry:Weather
A model of the ocean–atmosphere system that consists of a general circulation model of the atmosphere coupled with a model of the oceanic mixed layer. In climatic applications, the oceanic mixed layer is that part of the ocean that stores the seasonal heat anomaly and is typically represented in a very simple manner. Atmosphere–mixed layer ocean models are commonly used to study equilibrium climatic response.
Industry:Weather
1. A gaseous envelope gravitationally bound to a celestial body (e.g., a planet, its satellite, or a star). Different atmospheres have very different properties. For instance, the atmosphere of Venus is very thick and cloudy, and is responsible for producing the very high surface temperatures on that planet by virtue of its greenhouse effect. On the other hand, the Martian atmosphere is very sparse. Earth's atmosphere is intermediate between these two extremes. It is distinguished from all other known atmospheres by its very active hydrologic cycle. One need merely examine pictures of Earth from space to appreciate the intricate cloud structures. Water in Earth's atmosphere plays a very important energetic role. Because of its chemical composition, most incoming sunlight passes through Earth's atmosphere and is absorbed at the ground. This heat is transported to the atmosphere through sensible heat and moisture fluxes. Upon condensation, this heat is then released into the atmosphere. The thermodynamics of water vapor is the crucial factor to the existence of severe storms in Earth's atmosphere. Since more solar radiation is absorbed in the Tropics than at high latitudes, the atmosphere (and the ocean) transports heat poleward. These motions are heavily altered by the effects of planetary rotation to determine the atmospheric general circulation. Fluid dynamical instabilities play a large role in this circulation and are crucial in determining the fluctuations in this circulation that we call “weather. ”The atmosphere may be conceptually divided into several layers, according to its thermal and ionization structure. The region where the temperature decreases because of the upward heat flux is called the troposphere. Above it, there is a layer in which temperature increases upward because of ozone absorption of solar radiation, the stratosphere. Above this, the temperature decreases in the mesosphere, and above this, in the thermosphere, the extremely energetic radiation causes temperature to increase with height out to the outer reaches of Earth's atmosphere, the exosphere. Within the mesosphere and thermosphere, solar radiation is sufficiently energetic to ionize gases. This produces the ionosphere. 2. As a unit of pressure, see standard atmosphere. 3. See standard atmosphere, model atmosphere.
Industry:Weather
A device for measuring the frequency of occurrence of atmospherics, the intensity of which is greater than a predetermined level.
Industry:Weather
The general name for an instrument that measures the evaporation rate of water into the atmosphere. Four main classes of atmometers may be distinguished: 1) large evaporation tanks sunk into the ground or floating in water; 2) small evaporation pans; 3) porous porcelain bodies; and 4) porous paper wick devices. The evaporation from a surface depends greatly upon the nature of the surface and the exposure of the surface to the atmosphere. Measured evaporation rates should be compared only between identical instruments. See clay atmometer, evaporation pan, evapotranspirometer, Livingstone sphere, Piché evaporimeter, radio atmometer.
Industry:Weather
A water mass of Atlantic origin. In the Arctic Ocean the term is used for the water mass that enters the region from the Norwegian Sea and, on account of its high salinity, spreads underneath the fresher Arctic Surface Water. It can be followed as a salinity maximum at 150 m near Spitzbergen and progressively deeper to 500 m in the Canada basin. In the scattering, Atlantic Water identifies the water mass that enters through the Straits of Gibraltar and, on account of its lower temperature, spreads underneath the saltier but warmer Mediterranean surface water. It is seen as a salinity minimum at a depth of between 20 and 50 m.
Industry:Weather
