- 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, ...
A front presumed to exist within the equatorial trough separating the air of the Northern and Southern Hemispheres. It has been generally agreed that this front, if one exists, cannot be explained in the same terms as the fronts of higher latitudes. However, the extent to which frontal theory is to be modified and the nature of the modifications are as yet very controversial questions. See also intertropical convergence zone, doldrums.
Industry:Weather
A loop in the path of a parcel in inertial flow, which is approximately circular if the latitudinal displacement is small.
Industry:Weather
The horizontal pressure gradient per unit mass, −α∇Hp, where α is the specific volume, p the pressure, and ∇H the horizontal component of the del operator. This force acts normal to the horizontal isobars toward lower pressure. It is one of the three important forces appearing in the horizontal equations of motion, the others being the Coriolis force and friction. See pressure force.
Industry:Weather
After U. S. Weather observing practice, the ceiling classification applied when the reported ceiling value represents the vertical visibility upward into surface-based atmospheric phenomena (except precipitation). Such phenomena include fog, blowing snow, and all of the lithometeors. All indefinite ceilings are estimations, but one of the following must be used as a guide: 1) the distance an observer can see vertically into the obstruction; 2) the height corresponding to the top of a ceiling-light beam; 3) the height at which a ceiling balloon completely disappears; 4) the height determined by the sensor algorithm at automated stations. The letters “VV” (vertical visibility) are used to designate an indefinite ceiling.
Industry:Weather
A unit of luminous intensity, defined as a fixed fraction of the luminous intensity of a standardized electric lamp operated under prescribed conditions. The international candle was adopted as a more precise measure of the luminous intensity than the candle. It was replaced by the “new candle” in 1939, and finally the candela in 1948.
Industry:Weather
Any nonfrontal line or band of convective activity in the atmosphere. It is a general term and includes the developing, mature, and dissipating stages. However, when the mature stage consists of a line of active thunderstorms, it is properly called a squall line; therefore, in practice, instability line often refers to the less active phases. See also pseudo front, prefrontal squall line.
Industry:Weather
A strong wind and sandstorm or duststorm in northern and central Sudan, especially around Khartoum, where the average number is about 24 a year. The name comes from the Arabic word habb, meaning “wind. ” Haboobs are most frequent from May through September, especially in June, but they have occurred in every month except November. Their average duration is three hours; they are most severe in April and May when the soil is driest. They may approach from any direction, but most commonly from the north in winter and from the south, southeast, or east in summer. The average maximum wind velocity is over 13 m s−1 (30 mph) and a speed of 28 m s−1 (62 mph) has been recorded. The sand and dust form a dense whirling wall that may be 1000 m (3000 ft) high; it is often preceded by isolated dust whirls. During these storms, enormous quantities of sand are deposited. Haboobs usually occur after a few days of rising temperature and falling pressure.
Industry:Weather
A tropical cyclone with 1-min average surface (10 m) winds in excess of 32 m s−1 (64 knots) in the Western Hemisphere (North Atlantic Ocean, Caribbean Sea, Gulf of Mexico, and in the eastern and central North Pacific east of the date line). The name is derived from “huracan,” a Taino and Carib god, or “hunraken,” the Mayan storm god. For a more complete discussion, see tropical cyclone.
Industry:Weather
Indicating or having equal frequency or intensity of thunderstorm activity. See isoceraunic line, isobront.
Industry:Weather
