- 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, ...
That part of the air–earth current contributed by the electrical conduction of the atmosphere itself. It is represented as a downward current in storm-free regions all over the world. The conduction current is the largest portion of the air–earth current, far outweighing the contributions made by the precipitation current and convection current, which are zero in storm-free regions. Its magnitude is approximately 3 × 10−12 amperes (A) m−2, or about 1800 A for the entire earth. Such observations of the vertical variation of the conduction current as have been made indicate that it is approximately uniform throughout the depth of the troposphere, a condition that is consistent with the generally accepted view that the conduction current flows from a positively charged conducting region in the lower ionosphere downward to the negatively charged earth. Only in areas of temporarily disturbed weather does the conduction current become replaced by reverse flow. Accumulating evidence points to the conclusion that the conduction current continues to exist only because of the action of thunderstorms scattered at all times over the earth, which supply the positive charge to the upper atmosphere and negative charge to the earth. See supply current.
Industry:Weather
The continuation of the Alaska Current along the southern side of the Aleutian Islands. The distinction between the Alaskan Stream and the Alaska Current is gradual, and the two currents are sometimes regarded as one. They are, however, of different character, the Alaska Current being shallow and variable but the Alaskan Stream reaching to the ocean floor. Despite its modest speed of 0. 3 m s−1, it is a western boundary current. Most of the water of the Alaskan Stream feeds directly into the Oyashio. Some of its flow enters the Bering Sea between the Aleutian Islands (most of it between 168° and 172°W) and follows a cyclonic path before feeding into the Kamchatka Current, thus eventually also contributing to the Oyashio.
Industry:Weather
The eastern semi of the North Pacific subpolar gyre. It is a shallow current carrying relatively warm water northward and thus has a climate influence similar to that exercised by the North Atlantic and Norwegian Currents on the climates of northwestern Europe, though on a smaller scale. It flows cyclonically around the Gulf of Alaska, feeding into the Alaskan Stream. Freshwater from the many rivers of Canada and Alaska reduces the water density near the coast; the result is a pressure gradient normal to the coast that constrains the current geostrophically to the coastal region and increases its speed to 0. 3 m s−1.
Industry:Weather
Likelihood of or confidence in a forecast or report of dangerous, threatening, or damaging weather-related phenomena. For example, a warning or watch may be issued based on either a forecast or observation of severe thunderstorms, flash flooding, river flooding, high winds, winter storms, etc. The National Weather Service does not wait for the event to occur before warning the public; there must be some lead time associated with it, such as a flood warning prior to reaching flood stage.
Industry:Weather
Any one of the many microscopic particles in the atmosphere that serve as condensation nuclei for droplet growth in the large supersaturations (greater than a few hundred percent over water) produced during the rapid, near adiabatic expansion produced in an Aitken dust-counter. These nuclei, often numbering many tens of thousands per cubic centimeter in city air, are both solid and liquid particles with diameters on the order of tenths of microns or smaller. Because of the excessive supersaturations that accompany expansions of the air sample in an Aitken dust- counter, the nucleus spectrum observed with this instrument does not correspond to that observed in natural cloud condensation processes, where supersaturations larger than one per cent over water are probably rare. On the other hand, Aitken nuclei play an important role in determining the local electrical conductivity of the air, because they capture small ions, becoming large ions with much lower mobility in the earth's fair-weather electric field. In air containing large numbers of Aitken nuclei, the small ion population is small, the large ion population is large, and the air conductivity is low. Either nucleus may also be a protoparticle for larger particles such as cloud condensation nuclei, the subset of Aitken nuclei responsible for the formation of cloud droplets.
Industry:Weather
An instrument developed by John Aitken for determining the dust content of the atmosphere. A sample of air is mixed in an expandable chamber with a larger volume of dust-free air containing water vapor. Upon sudden expansion, the air in the chamber cools adiabatically below its dewpoint, and droplets form with the dust particles as nuclei. A portion of these droplets settle on a ruled plate in the instrument and are counted with the aid of a microscope. See dust counter.
Industry:Weather
A small instrument shelter designed for use at supplementary airways weather reporting stations (SAWRS). It is a white, louvered box mounted on a single post.
Industry:Weather
An officially designated air route with sectors defined as specific courses to or from directional radio stations.
Industry:Weather
The speed on an exposed (usually airborne) object relative to the atmosphere. In a calm atmosphere, airspeed equals ground speed.
Industry:Weather
A model designed to study and predict the air quality of a given region, usually of dimensions of the order of hundreds of kilometers. The models typically include sources of primary pollutants, the meteorology of the region being modeled, and a chemical scheme that describes the production of secondary pollutants. Airshed models of urban regions are the most common.
Industry:Weather
