- 업종: 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, ...
Part of an obsolete conceptual model of air parcel ascent referring to a portion of the ascent during which the parcel temperature remains at the freezing point until all the rain produced previously has frozen. Other portions of the ascent were described as the dry stage, snow stage, and rain stage.
Industry:Weather
One-half the scalar product of the velocity and vorticity vectors. It is a conserved quantity if the flow is inviscid and homogeneous in density, but is not conserved in more general viscous flows with buoyancy effects. The concept is useful in understanding severe convective storms and tornadoes, since in strong updrafts the velocity and vorticity vectors tend to be aligned, yielding high helicity. Three-dimensional turbulence containing a nonzero mean value of helicity may develop an inertial decay range, but the development is slowed by helicity. The reluctance of helical turbulence to cascade into an inertial range means that small-scale atmospheric flows with high helicity are less unstable and more predictable than small-scale flows with low helicity. See also storm-relative environmental helicity, streamwise vorticity.
Industry:Weather
Opaque, granular masses of rime deposited chiefly on vertical surfaces by a dense supercooled fog. Hard rime is more compact and amorphous than soft rime and may build out into the wind as glazed cones or ice feathers. The icing of ships and shoreline structures by supercooled spray from the sea usually has the characteristics of hard rime.
Industry:Weather
Organic compound, formula C5H8; 2–methyl–1,3–butadiene; it is the major hydrocarbon emitted by vegetation, particularly members of the oak genus. Emission rates depend on the leaf temperature and availability of sunlight. Isoprene is very reactive with the hydroxyl radical and with ozone, and its reactivity is thought to contribute to high levels of ozone found over the rural southeastern United States and other areas.
Industry:Weather
One of the many forms in which ice crystals are found in the atmosphere. This particular crystal habit of ice is characterized by hexagonal cross section in a plane perpendicular to the long direction (principal axis, optic axis, or c axis) of the columns. It differs from that found in hexagonal platelets only in that environmental conditions have favored growth along the principal axis rather than perpendicular to that axis. Growth by vapor deposition at temperatures of from −3° to about −8°C and also at lower temperature below −25°C leads to growth of columnar crystals, though other crystal features (needles, scrolls) also appear in this temperature interval, depending on the degree of water vapor supersaturation and the crystal fall velocity. See column.
Industry:Weather
One of several lines or planes used as reference for observation and measurement relative to a given location on the surface of the earth, and referred generally to a horizontal direction (i.e., at right angles to the zenith). Considerable contradiction exists between the nomenclatures for the several concepts of horizon. Aside from the distinctly different geological horizons (strata of earth material), it may be said that there are two types of horizons: earth–sky horizons (1, 2, and 3 below) and celestial horizons (4 and 5 below). Meteorology is primarily concerned with the former, astronomy with the latter. Specifically, the following constitute the major variant usages, with suggested nomenclature along with other names that have been applied. 1) Local horizon: the actual lower boundary of the observed sky or the upper outline of terrestrial objects including nearby natural obstructions. 2) Geographic horizon (also called apparent horizon, local horizon, visible horizon): the distant line along which earth and sky appear to meet. In both popular usage and weather observing, this is the usually conception of horizon. Nearby prominences are said to obscure the horizon and are not considered to be a part of it. The minimum desirable horizon distance should be of the order of three miles. 3) Sea level horizon (also called ideal horizon, sensible horizon, sea horizon, visible horizon, apparent horizon): the apparent junction of the sky and the sea level surface of the earth; the horizon as actually observed at sea. This type of horizon is used as the reference for establishing times of sunrise and sunset. 4) Astronomical horizon (also called sensible horizon, real horizon): the plane that passes through the observer's eye and is perpendicular to the zenith at that point; or, the intersection of that plane with the celestial sphere (i.e., a great circle on the celestial sphere equidistant from the observer's zenith and nadir). It is the projection of a horizontal plane in every direction from the point of orientation. 5) Celestial horizon (also called rational horizon, geometrical horizon, true horizon): the plane, through the center of the earth, that is perpendicular to a radius of the earth that passes through the point of observation on the earth's surface; or, the intersection of that plane with the celestial sphere. See also artificial horizon, fog horizon, haze horizon, smoke horizon.
Industry:Weather
On radar displays, a line or contour connecting all points of equal target signal strength or radar reflectivity factor, labeled, for example, in units of dBZ. Such displays for radar or lidar (e.g., PPI, RHI, THI) can be generated in real time using grayshades or colors to show steps in the reflectivity pattern. See echo contour.
Industry:Weather
Of the three standard turbulence length scales, the ones that are measures of the largest separation distance over which components of the eddy velocities at two distinct points are correlated. They characterize the energy-containing range of eddy length scales. In the most general form, the integral scales (expressed here as a tensor) are functions of position and are defined in terms of the normalized two-point velocity correlations. Compare Taylor microscale, Kolmogorov microscale.
Industry:Weather
On a given reference surface in space, a line connecting points of equal value of some quantity. Most of the lines drawn in the analysis of synoptic charts are isotimic lines. Compare isopleth.
Industry:Weather
