- 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, ...
In cloud physics, the process producing precipitation by collision and coalescence between liquid particles (cloud droplets, drizzle drops, and raindrops). Drop breakup is a limiting factor to large drop growth by this process.
Industry:Weather
In cloud physics, the merging of two water drops into a single larger drop after collision. Coalescence between colliding drops is affected by the impact energy, which tends to increase with the higher fall velocities of larger drops. Colliding drops having negligible impact energy compared to their surface energy behave as water spheres that collide with a collision efficiency (the fraction of small drops that collide with a large drop within the geometric collision cross section) predicted by the theory for falling spheres. The result of increasing impact energy is to flatten the colliding drops at the point of impact, impeding the drainage of the air and delaying contact between them. As the distortion relaxes, the drops rebound, reducing the coalescence efficiency for cloud drops and drizzle drops colliding with smaller drops. At larger impact energy, separation will occur if the rotational energy (fixed by conservation of angular momentum) is higher than the surface energy of the coalescing drops. This phenomenon, termed temporary coalescence, can result in satellite droplets considerably smaller than either of the parent drops. This phenomenon is also called partial coalescence because the large drop may gain mass as a result of the higher internal pressure in the small drop. At still larger impact energy, drop breakup occurs for the smaller drop. About 20% of the high-energy collisions between large raindrops (d > 3 mm) and drizzle drops (d > 0. 2 mm) result in the disintegration of both drops. Other factors that affect coalescence are electric charge and electric field, both of which promote coalescence, leading to earlier onset of coalescence during an interaction so that coalescence efficiencies are increased by suppression of rebound and temporary coalescence. All of these processes are important in formation of precipitation in all liquid clouds both above and below 0°C. See collision– coalescence process.
Industry:Weather
In cloud physics, for aerodynamically interacting cloud and precipitation particles: 1) for interacting water drops, the product of collision efficiency and coalescence efficiency; 2) for interacting ice particles, or for water drops interacting with ice particles, the product of collision efficiency and adhesion efficiency.
Industry:Weather
In Canada, a gale of Ellesmere Island so strong that it “blows the horns off the cows. ”
Industry:Weather
In aviation weather observation, a description or explanation of the manner in which the height of the ceiling is determined. The different types of ceilings according to this classification are aircraft ceiling, balloon ceiling, estimated ceiling, indefinite ceiling, measured ceiling, and precipitation ceiling.
Industry:Weather
In aviation terminology, the motion of an aircraft in flight when a crosswind causes its heading to differ from the course. See drift, drift-correction angle.
Industry:Weather
In aviation terminology, authorization for an aircraft to proceed under conditions specified by an air traffic control unit. For convenience, the term “air traffic control clearance” is frequently abbreviated to “clearance” when used in appropriate contexts. The abbreviated term “clearance” may be prefixed by the words “taxi,” “takeoff,” “departure,” “en route,” “approach,” or “landing” to indicate the particular portion of flight to which the air traffic clearance relates.
Industry:Weather
In atmospheric electricity, the electrical resistance of a column of air 1 m square, extending from the earth's surface to some specified altitude. Measurements extending to an altitude of 18 km indicate that the atmospheric columnar resistance to that height amounts to about 1017 ohm m−2. Probably, this is only slightly less than the total columnar resistance from earth to ionosphere. In fact, roughly half of the total columnar resistance from the earth to 18 km is contributed by the lowest 3 km of the column where, in addition to the greater density of the air, the high concentration of atmospheric particulates leads to a relatively high population of poorly conducting large ions rather than the more mobile small ions. Total columnar resistance does not vary greatly with either time or locality. By contrast, the columnar resistance of the lowest fraction of a kilometer varies greatly, causing fluctuations in the atmospheric electric field at sea level, especially in industrial areas of highly variable atmospheric pollution. See ion mobility.
Industry:Weather
In astronomy, the juxtaposition of the earth, sun, and one of the other planets or the moon, in which the angle subtended at the earth between the sun and the third body, in the plane of the ecliptic, is 0° (i.e., the third body lies either between the sun and the earth, or on the opposite side of the sun from the earth). Compare opposition, quadrature.
Industry:Weather
In a specified stream channel, the water depth at which the specific energy is the minimum for a given rate of flow. Critical depth usually occurs at the point corresponding to an abrupt steepening of channel slopes, such as rapids.
Industry:Weather
