- 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 crescent-shaped upper surface of a column of liquid. The curvature of this surface is dependent upon the cross-sectional area of the liquid and the relative ability of the liquid to wet the walls of the enclosure. For liquids that wet the walls of the enclosure, the curvature of the surface is concave. In the case of a mercury column enclosed in a glass container, the surface is convex, since mercury does not wet glass.
Industry:Weather
The temperature at which a solid substance undergoes fusion, that is, melts, changes from solid to liquid form. The melting point of a substance should be considered a property of its crystalline form only. At the melting point the liquid and solid forms of a substance exist in equilibrium. All substances of crystalline nature have their characteristic melting points. For very pure substances the temperature range over which the process of fusion occurs is very small. The melting point of a pure crystalline solid is a function of pressure; it increases with increasing pressure for most substances. However, in the case of ice (and a few other substances) the melting point decreases with increasing pressure (see regelation). Under a pressure of one standard atmosphere, the melting point of pure ice is the same as the ice point, that is, 0°C. Compare freezing point.
Industry:Weather
The altitude at which ice crystals and snowflakes begin to melt as they descend through the atmosphere. In cloud physics and in radar meteorology, this is the accepted term for the 0°C constant-temperature surface (see bright band). It is physically more apt than the corresponding operational term, freezing level, for melting of pure ice must begin very near 0°C, but freezing of liquid water can occur over a broad range of temperatures (between 0° and −40°C; see supercooling). See also freezing point, ice point, melting point.
Industry:Weather
The altitude interval throughout which ice-phase precipitation melts as it descends. The top of the melting layer is the melting level. The melting layer may be several hundred meters deep, reflecting the time it takes for all the hydrometeors to undergo the transition from solid to liquid phase. The temperature of the melting layer is typically 0°C or slightly warmer. See bright band.
Industry:Weather
A pond of liquid water (mostly from melted snow) on the surface of sea ice, usually occurring in the spring. Melt ponds are common in the Arctic but less so in the Antarctic.
Industry:Weather
A forecast for a period extending from about three days to seven days in advance; there are no absolute limits to the period embraced by the definition. Compare long-range forecast, extended forecast.
Industry:Weather
Coherent subsurface masses of anticyclonically rotating, warm salty water in the Atlantic Ocean originating from the Mediterranean Sea. These mesoscale lenses have been observed to persist for up to many months. See Meddy.
Industry:Weather
A quasi-persistent, nearly stationary, east–west-oriented weak baroclinic zone in the lower troposphere that typically stretches from the east China coast, across Taiwan, and eastward into the Pacific, south of Japan. The term “mei-yu” is the Chinese expression for “plum rains. ”
The mei-yu front generally occurs from mid- to late spring through early to midsummer. This low-level baroclinic zone typically lies beneath a confluent jet entrance region aloft situated downstream of the Tibetan Plateau. The mei-yu/baiu front is very significant in the weather and climate of southeast Asia as it serves as the focus for persistent heavy convective rainfall associated with mesoscale convective complexes (MCCs) or mesoscale convective systems (MCSs) that propagate eastward along the baroclinic zone. The moisture source is typically the South China Sea and sometimes the Bay of Bengal. The usual lifting mechanism is low-level warm-air advection in association with a low-level jet on the equatorward flank of the baroclinic zone. Deep ascent and resulting organized MCCs/MCSs are especially favored when the low-level warm-air advection is situated beneath the favorable equatorward jet entrance region aloft.
Industry:Weather
A unit of frequency equal to one million (10<sup>6</sup>) cycles per second.
Industry:Weather
A type of climate characterized by continuous high temperatures in combination with abundant rainfall (in excess of evapotranspiration) throughout the year. This climate is the type required to support the growth of the plant group known as megatherms. This is an (A) climate under the Köppen classification (1931) and, as defined by Thornthwaite's climatic classification scheme (1948), this is a climate with annual potential evapotranspiration in excess of 114 cm. Compare mesothermal climate, microthermal climate.
Industry:Weather
