- Industry: Weather
- Number of terms: 60695
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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, ...
Any storm that produces hailstones that fall to the ground; usually used when the amount or size of the hail is considered significant.
Industry:Weather
Any polar area permanently covered by ice and snow, with no vegetation other than occasional red snow or green snow.
Industry:Weather
Any product of condensation or deposition of atmospheric water vapor, whether formed in the free atmosphere or at the earth's surface; also, any water particle blown by the wind from the earth's surface. Hydrometeors may be classified in a number of different ways, of which the following is one example: 1) liquid or solid water particles formed and remaining suspended in the air, for example, damp (high relative humidity) haze, cloud, fog, ice fog, and mist; 2) liquid precipitation, for example, drizzle and rain; 3) freezing precipitation, for example, freezing drizzle and freezing rain; 4) solid (frozen) precipitation, for example, snow, hail, ice pellets, snow pellets (soft hail, graupel), snow grains, and ice crystals; 5) falling particles that evaporate before reaching the ground, for example, virga; 6) liquid or solid water particles lifted by the wind from the earth's surface, for example, drifting snow, blowing snow, and blowing spray.
Industry:Weather
Any particle that serves as a nucleus leading to the formation of ice crystals without regard to the particular physical processes involved in the nucleation. The process is referred to as heterogeneous nucleation, as opposed to homogeneous nucleation, which depends on the formation of an ice particle large enough to grow by random motion of water molecules alone. Four processes are generally distinguished: 1) deposition (sorption; previously called sublimation), where the ice phase forms directly from water vapor; 2) condensation freezing, where the ice phase forms in a supercooled solution following growth and dilution of a cloud condensation nucleus; 3) contact freezing, where a supercooled droplet nucleates following contact of an ice nucleating aerosol; 4) immersion freezing, where the nucleating particle is completely immersed in the supercooled liquid, which nucleates with sufficient cooling. Because of this multiplicity of nucleation mechanisms it is often difficult to deduce the processes active in a given cloud. Artificially generated aerosols such as silver iodide show activity by all four mechanisms, but at different rates. For natural ice nucleating aerosols, activities in all modes do not generally occur. Observations strongly suggest that, whatever their physico-chemical nature, most natural nuclei act through a freezing process rather than by deposition.
Industry:Weather
Any one of a number of macroscopic, crystalline forms in which ice appears, including hexagonal columns, hexagonal platelets, dendritic crystals, ice needles, and combinations of these forms. The crystal lattice of ice is hexagonal in its symmetry under most atmospheric conditions. Varying conditions of temperature and vapor pressure can lead to growth of crystalline forms in which the simple hexagonal pattern is present in widely different habits (a thin hexagonal plate or a long thin hexagonal column). In many ice crystals, trigonal symmetry can be observed, suggesting an influence of a cubic symmetry. The principal axis (c axis) of a single crystal of ice is perpendicular to the axis of hexagonal symmetry. Planes perpendicular to this axis are called basal planes (a axes related to the prism facets) and present a hexagonal cross section. Ice is anisotropic in both its optical and electrical properties and has a high dielectric constant (even higher than water) resulting from its water dipole structure. The electrical relaxation time for water is much shorter than for ice (109 Hz compared with 104 Hz), resulting from a chain reaction requirement for molecules to relax through defects in the ice lattice. In the free air, ice crystals compose cirrus-type clouds, and near the ground they form the hydrometeor called, remarkably enough, “ice crystals” (or ice prisms). They are one constituent of ice fog, the other constituent being droxtals. On terrestrial objects the ice crystal is the elemental unit of hoarfrost in all of its various forms. Ice crystals that form in slightly supercooled water are termed frazil. Ice originating as frozen water (e.g., hail, graupel, and lake ice) still has hexagonal symmetry but lacks any external hexagonal form. Analysis of their sections (0. 5 mm) in polarized light reveals different crystal shapes and orientations, depending on the freezing and any annealing and subsequent recrystallization process.
Industry:Weather
Any of those variables of a problem, chosen according to convenience, that may arbitrarily be specified, and that then determine the other or dependent variables of the problem. The independent variables are often called the coordinates, particularly in problems involving motion in space. Dependent and independent variables can be interchanged, for example, height and pressure.
Industry:Weather
Any of a family of colored or whitish rings, arcs, pillars or spots of light that appear in the sky and are explained by the reflection or refraction of light by ice crystals. They are usually found in the vicinity of the light source, the most important of which are the sun and moon, but may arise from artificial lights if seen, say, through an ice fog. Halos exhibiting some prismatic coloration are explained, at least in part, by the refraction of light by the ice crystals. However, the color is usually fairly pale, being best on a red edge next to the light. The exceptions, in having very good colors, are the circumhorizontal and circumzenithal arcs, the positions of which are not determined by the minimum angle of refraction. Halos that are white, or show the same color as the light source itself, are explained by the reflection of light off the crystal faces. Whether explained by reflection or refraction, the pattern that emerges depends upon the crystal type, crystal orientation (actually the probability of various orientations within a population of crystals), and the elevation angle of the light (sun). With such a rich range of possibilities, a large variety of halos are theoretically possible and over 50 different halo phenomena have been documented photographically. Some halos predicted theoretically have yet to be reported, others that have been reported have yet to be explained. The most common halo is the halo of 22°. Other frequently seen halos are the parhelia of the halo of 22°, the sun pillar, the 22° tangent arcs, the circumzenithal arc, the halo of 46°, and the parhelic circle. On very rare occasions an observer's sky will be filled with a display with 10, 20, or more different halos, usually persisting for only a few minutes. Much supernatural lore has been prompted by observations of old of such events. Halos must be distinguished from optical phenomena arising from water drops, such as the rainbow, corona, and glory.
Industry:Weather
Any method that modifies observed atmospheric initial conditions so that high- frequency oscillations are removed from a subsequent forecast with an NWP model. See dynamic initialization, normal mode initialization.
Industry:Weather
Any instrument that measures the water vapor content of the atmosphere. There are six basically different means of transduction used in measuring this quantity and hence an equal number of types of hygrometers. These are 1) the psychrometer, which utilizes the thermodynamic method; 2) the class of instruments that depends upon a change of physical dimensions due to the absorption of moisture (see hair hygrometer, torsion hygrometer, goldbeater's-skin hygrometer); 3) those that depend upon condensation of moisture (see dewpoint hygrometer, frost point hygrometer); 4) the class of instruments that depend upon the change of chemical or electrical properties due to the absorption of moisture (see absorption hygrometer, electrical hygrometer, carbon-film hygrometer element, dew cell); 5) the class of instruments that depend upon the diffusion of water vapor through a porous membrane (see diffusion hygrometer); and 6) the class of instruments that depend upon measurements of the absorption spectra of water vapor (see spectral hygrometer).
Industry:Weather
