- 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 modeling technique that describes the height dependence of meteorological parameters in the upper part of the atmospheric boundary layer by (''z''/''z''<sub>0</sub>)(Ro)<sup>−1</sup>, where ''z''<sub>0</sub> is the surface roughness length and Ro = ''u''<sub>*</sub>/''fz''<sub>0</sub> is called the friction Rossby number, where ''f'' is the Coriolis parameter and ''u''<sub>*</sub> is the friction velocity. Other Rossby numbers are also used, always in the form of a velocity scale divided by the product of a length times the Coriolis parameter.
Industry:Weather
A model of the clear atmosphere used for light scattering calculations. A pure Rayleigh atmosphere contains only the permanent atmospheric gases that scatter light by Rayleigh scattering. It excludes the effects of water vapor, clouds, and aerosols.
Industry:Weather
A model of a system that includes some sort of random forcing. In many cases, stochastic models are used to simulate deterministic systems that include smaller- scale phenomena that cannot be accurately observed or modeled. As such, these small-scale phenomena are effectively unpredictable. A good stochastic model manages to represent the average effect of unresolved phenomena on larger-scale phenomena in terms of a random forcing.
Industry:Weather
A model of a surface or bottom mixed layer in which all quantities (scalar and vector) are assumed to be completely and instantaneously homogenized. The assumption is that the processes affecting the mixed layer as a whole act slowly in comparison to the mixing time of the large eddies that stir the layer. See'' also'' mixed-layer models, jump model.
Industry:Weather
A model in which the prognostic field variables are represented as sums of a finite set of spectral modes rather than at gridpoints. The spectral modes may be Fourier modes in the one-dimensional case or double Fourier modes or spherical harmonics in the two-dimensional case. The advantage of a spectral model is that horizontal derivatives can be calculated exactly for the spectral modes represented in the model and thus the model error is confined only to the unrepresented higher spectral modes beyond the model's spectral truncation.
Industry:Weather
A mirrorlike surface for which the angle of reflection equals the angle of incidence; to be contrasted with a diffuse reflector. Most natural surfaces are too irregular to act as good specular reflectors of solar radiation, the main exception being calm water surfaces.
Industry:Weather
A mirage in which the image or images are displaced upward from the position of the object. If only a single image of distant objects is seen, then the term looming is often applied: A horizontal surface appears to curve upward with increasing distance and terminate in a relatively distant optical horizon. The looming might be accompanied by either stooping or towering. The superior mirage is most striking when it exhibits three or more images. The upper and lower images are always erect, while a single middle image will be inverted. No matter the number, images will alternate between erect and inverted, although sometimes a pair will appear back to back and might be interpreted as a single image. Although textbooks sometimes suggest that what is seen is an object and an even number of images, all are images, and have positions and magnifications that differ from that of the object. What is seen is dependent upon both the distance to objects and the height of the eye. A change of either can produce markedly different image characteristics. Superior mirages occur over a surface when (molecular number) density decreases with height, but are always most striking when temperature increases with height. Then, what is seen (for a particular distance and observing height) depends critically on the shape of the temperature (and thus, the refractive index) profile. Everything from stooping to towering to multiple images is a possible result of fairly simple profiles. A common profile, a lifted temperature inversion, can not only produce the three-image mirage but, since internal gravity waves often occur on such an inversion, the resulting periodic horizontal inhomogeneity can also produce a higher number of images. Such lifted inversions are common over, but hardly confined to, enclosed bodies of water on warm afternoons when the warmer air from the surrounding land flows over the colder water. Compare inferior mirage, sinking.
Industry:Weather
A method of obtaining information about properties of an object without coming into physical contact with that object.
Industry:Weather
A method of surveying the bottom of the ocean or other body of water to obtain detailed acoustic images, frequently used to locate debris, such as from aircraft accidents or sunken ships. The acoustic beam is directed perpendicularly to the direction of travel. The ship moves at a constant velocity, and each sonar ping insonifies a slightly different wedge of bottom. The apparent depth is actually the slant range from the ship to the target. The display is a map of slant range and distance along the track.
Industry:Weather
A mirage in which the image of distant objects is displaced downward. Because the displacement increases with distance, a horizontal surface, such as that of a body of water, desert, or road, appears to bend downward and one's perception is that of being on top of an inverted bowl or possibly on a planet with a very much smaller radius. Indeed, the downward bending surface results in an (optical) horizon that can be very much closer to the observer than in the absence of a mirage. Sinking is an example of an inferior mirage. The opposite of sinking is looming. Sinking occurs when the concave side of light rays from a distant object is up, and this in turn occurs when the refractive index of the atmosphere increases with height. This only happens near a surface when the heat flux is upward and so the temperature gradient decreases with height. This is common over a warm surface (such as might occur over sun-warmed ground or a lake at night). Sinking is often accompanied by a two-image inferior mirage. Compare stooping.
Industry:Weather
