- المجال: 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 lightning pattern revealed in cloud-to-ground lightning locations in which areas of predominantly negative flash locations are separated horizontally from positive flash locations. This pattern has been identified in midlatitude mesoscale convective systems (MCSs). The convective regions of the MCSs (those with radar echoes greater than 35 dBZ) typically have negative lightning flashes, whereas the positive flashes are typically located in the stratiform region (<35 dBZ) adjacent to the convective region. The bipolar pattern is hypothesized to arise from 1) the advection of positively charged particles from the upper portions of the convective region to the stratiform region due to vertical wind shear; 2) in situ charging of ice particles that acquire positive charge in an environment of supercooled liquid water and mesoscale ascent in the stratiform cloud layer; or 3) some combination of the two processes.
Industry:Weather
A jet on the windward side of a mountain barrier, blowing parallel to the barrier. The jet is produced when stable synoptic flow at low levels approaches the barrier and is blocked (see blocking) for a significant fraction of a day or longer. This often occurs, for example, when a cold front approaches the barrier. The component of the large-scale flow perpendicular to the ridge forces the flow to ascend the barrier. Because the air column is stable, the air layer near the surface is potentially colder (by definition) than the air layer above it, and the stratification opposes and retards the upslope flow. As the colder air ascends, it produces higher pressure along the slope than at the same level over the plain, and consequently also a pressure-gradient force directed away from the mountains. If this pressure configuration lasts for several hours or more, Coriolis deflection accelerates the flow with a component perpendicular to the pressure gradient, that is, in the along-barrier direction. At timescales greater than a pendulum day.
Industry:Weather
A hypothetical body that cannot be excited to radiate by an external source of electromagnetic radiation of any frequency, direction, or state of polarization except in a negligibly small set of directions around that of the source radiation. The traditional definition of a blackbody.
Industry:Weather
A hydrodynamic instability arising from the existence of a meridional temperature gradient (and hence vertical shear of the mean flow and a thermal wind) in an atmosphere in quasigeostrophic equilibrium and possessing static stability. For reasonable values of the atmospheric parameters, the wavelength of maximum instability corresponds to that of a synoptic-scale disturbance. Such a system may be interpreted as converting potential energy of the basic flow into kinetic energy of the unstable perturbation.
Industry:Weather
A height scale for turbulent flow above an inhomogeneous surface, at which the influences of individual surface patches on vertical profiles or fluxes become horizontally blended. Below this height scale it is not permissible to treat the structure of turbulence as horizontally uniform. Some authors distinguish between 1) the physical blending height, where local perturbations become negligible due to turbulent mixing, and 2) the numerical blending height in numerical models, above which the horizontal average of locally variable profiles (e.g., wind speed) corresponds to a similarity profile. Both of these height scales are related to the length scale of horizontal surface variations and, typically, the physical blending height is an order of magnitude higher than the numerical blending height. See effective roughness length, flux aggregation.
Industry:Weather
A haze that appears in the afternoons on the coast of Chile when sea air is transported inland.
Industry:Weather
A halo in the form of one or more rings or brightness plateaus immediately surrounding the subsun. The variation in brightness between the central subsun and the first ring is explained by the way the reflecting crystals oscillate as they fall.
Industry:Weather
A geometry in which the acoustic source and receiver are not at the same position.
Industry:Weather
A gastight compartment of variable volume to control ascent and descent and to maintain pressure in a nonrigid airship. When the ballonet is used within a superpressure balloon, valving of gas increases altitude, and pumping of air into the ballonet causes the balloon to descend. The superpressure is only marginally affected as the balloon changes altitude.
Industry:Weather
A function describing the anisotropy of reflected radiance from a surface illuminated from a single direction. It is equal to π times the reflected radiance divided by the incident irradiance from a single direction.
Industry:Weather
