- 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, ...
The precedence of a thaw in a valley, sometimes by many hours, by a thaw or marked rise in temperature at mountain level in the same vicinity. The phenomenon is usually caused by the arrival at higher levels of the warm air in advance of a surface warm front. It may also be caused by the subsidence and dynamical heating of air at the higher level. The associated inversion of the normal temperature lapse rate is a contributory cause of glaze.
Industry:Weather
The portion of the cooling of a human body caused by air motion. Air motion accelerates the rate of heat transfer from a human body to the surrounding atmosphere, especially when temperatures are below about 7°C (45°F).
Industry:Weather
The polynomial obtained by truncation of a Taylor series after a finite number of terms. See Taylor's theorem.
Industry:Weather
The poleward limit of tree growth; the botanical boundary between tundra and boreal forest. The arctic tree line has been studied extensively, but in the Southern Hemisphere, a “tree line” can be inferred only by comparison of vegetation on islands in the southern oceans. See Also timber line.
Industry:Weather
The pictorial representation of the shape of a wave showing the amplitude variations as a function of time; a wave as it might be displayed on a cathode-ray tube.
Industry:Weather
The period from approximately 10 800 to 9600 BC when climate in the region around Greenland cooled by 5°–7°C within a few decades and recovered with similar rapidity at the end of the period; named for the expansion of the geographic range of the arctic herb ''Dryas octopetala''. Evidence is accumulating for a wider, perhaps global, extent, but the Younger Dryas was most strongly felt around the North Atlantic Ocean. Changes in the thermohaline circulation of the oceans are widely believed to be implicated in the onset and ending of the Younger Dryas cooling. These were in turn associated with a switch to the St. Lawrence River as the major route for meltwater reaching the North Atlantic from the retreating continental ice cap. Other similarly rapid oscillations in climate are recorded through much of the last glacial in ice cores from Greenland and in marine sediment cores from the North Atlantic (Dansgaard–Oeschger events). The period since the Younger Dryas (the Holocene) lacks such extreme excursions.
Industry:Weather
The period after sunset or before sunrise when all or part of the sky is visibly bright because of sunlight scattered by clouds or the clear sky. Twilight also refers to the sky's appearance during this period. By convention, there are three sequential stages of twilight: civil twilight, nautical twilight, and astronomical twilight. (Some definitions of twilight set its upper limit as high as sun elevations ''h''<sub>0</sub> = 5°–10°. ) Regardless of cloud cover, illuminance at the earth's surface decreases steadily during evening twilight and increases during morning twilight. However, under partly cloudy or overcast skies, some minor brightness fluctuations can occur as twilight progresses. The color and luminance patterns of clear skies change in complex ways throughout twilight (see bright segment, dark segment, purple light), while overcast skies usually grow bluer during evening civil twilight. The length of nautical, astronomical, and civil twilight varies greatly with latitude and time of year. The annual range of the duration of twilight increases with latitude. For example, at polar latitudes twilight may last as long as 24 hours or may not occur at all. Compare dawn, dusk.
Industry:Weather
The open northern part of the boreal forest. It consists of open woodland of coniferous trees growing in a rich floor of lichen (mainly reindeer moss or caribou moss), and is generally cold and swampy. The taiga lies immediately south of the tundra. In spring, it is often flooded by water from northward flowing rivers, the lower reaches of which are still frozen.
Industry:Weather
The notable valley wind that blows along the Rhône valley from the upper end of Lake Geneva (Valais Canton). It is sufficiently strong and regular to distort the growth of trees.
Industry:Weather
