- 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 radar scanning pattern defined by a fixed plane tilted from the horizontal. Two radars performing dual-Doppler measurements typically scan a coplane that contains both radars and is tilted a few degrees from horizontal. The azimuth and elevation angles of each radar must be varied simultaneously and in a coordinated way to scan the coplane.
Industry:Weather
A radar echo with phase and amplitude either showing little change over successive radar pulses or changing in a regular and predictable way. Such an echo may arise from fixed or slowly moving point targets or from distributed targets in which the individual scattering elements do not move (or move slowly) with respect to one another. By contrast, an incoherent echo is an echo with random phase and amplitude from pulse to pulse. Such echoes arise from distributed targets such as precipitation targets, in which the individual scatterers move with respect to one another.
Industry:Weather
A radar echo returned from a region of the atmosphere with no apparent meteorological scatterers such as clouds or precipitation. Clear-air echoes are caused by either 1) solid target returns from birds, insects, dust, or other particulate matter, or 2) spatial fluctuations of refractivity with scale sizes on the order of or smaller than the radar wavelength. Two examples of the latter type of echo are Bragg scattering from atmospheric turbulence and Fresnel reflection or specular reflection from layers with sharp gradients in refractivity. Insects, birds, and particulates are the principal cause of clear-air echoes observed with radars having wavelengths of 3 cm or less, whereas high-powered radars operating at wavelengths of 10 cm or greater routinely detect backscattered signals from strong refractive index fluctuations. Compare angel.
Industry:Weather
A radar designed for detection of cloud particles as distinguished from the larger particles that constitute precipitation. Cloud radars typically employ short wavelengths of 1 cm and shorter (e.g., Ka band) and are designed for short-range, high-resolution measurements. They can also be multiwavelength or polarimetric radars capable of providing information on the shapes and sizes of the cloud particles. Radars operating at short wavelengths have increased sensitivity to all weather targets but also suffer from increased attenuation by clouds and precipitation.
Industry:Weather
A question and answer session with a knowledge-based system. It is often used in meteorological applications that require judgment on the part of the user.
Industry:Weather
A rabal observation (i.e., a radiosonde balloon tracked by theodolite) taken simultaneously with the usual rawin observation (tracking by radar or radio direction-finder). Its purpose is to provide a rough check on the alignment and operating accuracy of the electronic tracking equipment.
Industry:Weather
A quantity specified by components that transform according to prescribed rules under rotations of (Cartesian) coordinate axes. A Cartesian tensor of rank zero is a scalar and is invariant under rotations. A Cartesian tensor of rank one is a vector, the components of which transform under rotations according to a single 3×3 rotation matrix. Cartesian tensors of rank two have nine components that transform according to a product of two 3×3 rotation matrices. Tensors of higher rank may be defined in similar fashion. As examples related to meteorology, mass is a scalar, velocity is a vector, and the stress tensor is a Cartesian tensor of rank two. (Because of the restriction to transformation under rotation, a Cartesian tensor need not be a (general) tensor. The latter has components that transform in a prescribed way under arbitrary changes of coordinates. )
Industry:Weather
A property with values that do not change in the course of a particular series of events. Properties can be judged conservative only when the events (processes) are specified; also, properties that are conservative for a whole system may or may not be conservative for its parts, and conversely. Applied to airmass properties, this term is relative.
Industry:Weather
A quantity in the kinetic theory of gases that measures the tendency of gases to diffuse into one another in nonturbulent flow. This diffusion coefficient is a property of the gases in question and of the assumed nature of the molecular impacts in the diffusion process.
Industry:Weather
A property attributed to clouds (regarded in analogy to colloidal systems or aerosols) by virtue of which the particles of the cloud tend to aggregate (through Brownian motion) into masses large enough to precipitate. The viewpoint that regards an atmospheric cloud as an aerosol somewhat strains the physical chemist's definition thereof, for cloud particles are much larger than the particles typically treated as colloidally dispersed materials either in a gas or in a liquid.
Industry:Weather
