- 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, ...
1. An instrument for showing direction consisting of a magnetic needle or drum swinging freely on a pivot and pointing toward the earth's north magnetic pole. The instrument contains a viewing surface marked with points of direction and/or degrees of a circle. 2. A drawing instrument used to make circles or circular arcs.
Industry:Weather
1. An equation defining the characteristics of a set of partial differential equations. 2. A linear algebraic equation determining the eigenvalues (see characteristic-value problem) or free waves of a boundary-value problem.
Industry:Weather
1. After U. S. Weather observing practice, the state of the sky when it is cloudless or when the sky cover is less than 0. 1 (to the nearest tenth. )
In aviation weather observations, a clear sky state is denoted by the symbol “O. ” 2. The character of the sunrise or sunset when the disk of the sun is visible at these times. Compare cloudy. 3. To change from a stormy or cloudy weather condition to one of no precipitation and decreased cloudiness. 4. In popular usage, the condition of the atmosphere when it is very transparent (as opposed to hazy, foggy, etc. ) and accompanied by negligible cloudiness. In weather forecast terminology, the maximum cloudiness considered is about 0. 2. Compare cloudy, fair.
Industry:Weather
1. Air that is devoid of clouds or fog. 2. In some contexts, air that is devoid of any solid or liquid particles that would reduce visibility.
Industry:Weather
1. Altitude at which the relative horizontal phase speed of internal gravity waves equals the wind speed. As waves approach this altitude from above or below, the vertical component of group velocity approaches zero, causing elimination of the wave as its energy is absorbed and transferred to the mean wind. This causes changes in the wind-speed profile, which in turn can raise or lower the altitude of the critical level. 2. Altitude at which the wind shear is sufficiently strong to cause the gradient Richardson number to drop below its critical value, allowing Kelvin–Helmholtz waves to form. These breaking waves can generate propagating internal gravity waves in the adjacent air above and below. See buoyancy wave. 3. The level at which the ocean surface wave phase speed is equal to the wind (or current) speed. Considerable interaction between the wave field and the mean flow field can be associated with processes at this level. 4. See critical level of escape.
Industry:Weather
1. An adjustment of soil particles, in response to compressive stress, that results in lower porosity. 2. Any process that increases the firmness or coherence of a loose, soft, or liquid earth material, including cementation, compaction, and crystallization. 3. Decrease of the volume of an aquifer due to pumping and lowering of the water pressure that leads to the transfer of stress from interstitial water to aquifer solids.
Industry:Weather
1. After U. S. Weather observing practice, the height ascribed to the lowest layer of clouds or obscuring phenomena when it is reported as broken, overcast, or obscuration and not classified “thin” or “partial. ” The ceiling is termed unlimited when the foregoing conditions are not satisfied. Whenever the height of a cirriform cloud layer is unknown, a slant / is reported in lieu of a height value. At all other times, the ceiling is expressed in feet above the surface, which is a horizontal plane with an elevation above sea level equal to the airport elevation. At stations where this does not apply, “surface” refers to the ground elevation at the point of observation. For obscurations, the ceiling height represents vertical visibility into the obscuring phenomena rather than the height of the base, as in the case of clouds or obscuring phenomena aloft. In an aviation weather observation, the ceiling height is always preceded by a letter that designates the ceiling classification. 2. The greatest altitude to which an airborne object (aircraft, balloon, rocket, projectile, etc. ) can rise, under a given set of conditions. The ceiling of an aircraft is that altitude where the stalling Mach number and the buffeting Mach number approach identical value.
Industry:Weather
1. A unit measure of electrical conduction; the facility with which a substance conducts electricity, as represented by the current density per unit electrical-potential gradient in the direction of flow. Electrical conductivity is the reciprocal of electrical resistivity and is expressed in units such as mhos (reciprocal ohms) cm−1. It is an intrinsic property of a given type of material under given physical conditions (dependent mostly upon temperature). Conductance, on the other hand, varies with the dimensions of the conducting system, and is the reciprocal of the electrical resistance. 2. See thermal conductivity, thermometric conductivity. 3. See eddy conductivity.
Industry:Weather
1. A visible aggregate of minute water droplets and/or ice particles in the atmosphere above the earth's surface. Cloud differs from fog only in that the latter is, by definition, close (a few meters) to the earth's surface. Clouds form in the free atmosphere as a result of condensation of water vapor in rising currents of air, or by the evaporation of the lowest stratum of fog. For condensation to occur at a low degree of supersaturation, there must be an abundance of cloud condensation nuclei for water clouds, or ice nuclei for ice-crystal clouds, at temperatures substantially above −40°C. The size of cloud drops varies from one cloud type to another, and within any given cloud there always exists a finite range of sizes. Generally, cloud drops (droplets) range from 1–100 μm in diameter, and hence are very much smaller than raindrops. See cloud classification. 2. Any collection of particulate matter in the atmosphere dense enough to be perceptible to the eye, as a dust cloud or smoke cloud.
Industry:Weather
1. A set of one or more colored rings of small angular radii concentrically surrounding the the sun, moon, or other light source when veiled by a thin cloud. The corona can be distinguished from the halo of 22° due to its much smaller angular radius, which is often only a few degrees, and by its color sequence, which is from bluish white on the inside to reddish on the outside, the reverse of that in the 22° halo. Further, the color sequence of the corona can be repeated. Fraunhofer diffraction theory is often used to provide an approximate description of the corona. This theory predicts that the center of the corona is essentially white and that the radius of a ring of a particular color is approximately inversely proportional to the drop radius. Consequences of this are that the rings are most discernible and have the purest colors when the droplets in a particular portion of a cloud are nearly uniform in size (mono disperse); the rings are most nearly circular if the droplets that produce different portions of the corona are nearly the same size (spatial homogeneity); rings are caused by droplets with a radius of less than about 15 μm (the rings from larger droplets are washed out by the angular width of the sun). When there is a broad range of droplet sizes, the rings are distinct, the colors faint, and the phenomenon is often called an aureole. Although it is possible for colorful coronas to be produced by ice crystals, usually the broad range of sizes and shapes of crystals precludes this. Similarly, coronas are rarely produced by dust due to the broad range of particle sizes normally present, but rare observations, such as Bishop's rings, have been reported. 2. (Also called solar corona. ) The outer envelope of the sun's atmosphere consisting of ionized gases, predominantly hydrogen and helium, at temperatures that exceed one million degrees Kelvin. The white light emission observed at solar eclipse or with the coronagraph arises from scattering of photospheric radiation from free electrons in the corona. The shape of the corona varies during the sunspot cycle. At solar minimum the corona has large extensions along the sun's equator, with short brush-like tufts near the poles. At solar maximum the equatorial extensions are much smaller and the corona is more regular in shape. 3. See aurora. 4. See corona discharge.
Industry:Weather
