- 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 regular pattern of convective cells that can develop in an atmospheric boundary layer heated from below or radiatively cooled from cloud top. This phenomenon is readily observed in satellite imagery during cold air outbreaks when continental air passes over the relatively warm coastal ocean. Cloud lines, marking horizontal roll vortices, form initially in the developing marine atmospheric boundary layer. These lines evolve into open cells, which are defined by clouds in the upward motion along the edges of honeycomb- shaped cells, with less cloudy subsiding air in their centers. The convective structure further evolves into closed cells, which have cloudy centers and cloud-free edges.
Industry:Weather
Pertaining to atmospheric phenomena having horizontal scales ranging from a few to several hundred kilometers, including thunderstorms, squall lines, fronts, precipitation bands in tropical and extratropical cyclones, and topographically generated weather systems such as mountain waves and sea and land breezes. From a dynamical perspective, this term pertains to processes with timescales ranging from the inverse of the Brunt–Väisälä frequency to a pendulum day, encompassing deep moist convection and the full spectrum of inertio-gravity waves but stopping short of synoptic-scale phenomena, which have Rossby numbers less than 1.
Industry:Weather
A plant that grows under conditions of a medium amount of water; temperature is not a limiting factor.
Industry:Weather
The top of the mesosphere and the base of the thermosphere. The mesopause is usually located at heights of 85–95 km, and is the site of the coldest temperatures in the atmosphere. Temperatures as low as 100 K (− 173°C) have been measured at the mesopause by rockets. See atmospheric shell.
Industry:Weather
A low pressure area on the mesoscale. It has been used to refer both to features observed within convective storms and features even larger in scale.
Industry:Weather
A mesoscale wind maximum. It typically may have an along-flow length scale of tens to hundreds of kilometers and a cross- flow length scale of < 100 km. Mesojets differ from planetary-scale jets, which can have length scales of several thousand kilometers, and synoptic-scale jets, which may have length scales of 1000– 2000 km and are commonly found in association with progressive synoptic-scale troughs and ridges. Larger mesojets may also sometimes be known as jet streaks. Mesojets can form adjacent to prominent orographic features in association with terrain-channeled flow. Mesojets are also seen in association with organized mesocale convective systems as typified by the evaporatively driven rear-inflow jet commonly found behind active squall lines lines. Mesojets may also be found in conjunction with prominent lower-tropospheric stable layers where the airflow can become decoupled from the planetary boundary layer, especially at night. An exceptionally well organized lower-tropospheric mesojet extending over hundreds of kilometers might be known as a low-level jet.
Industry:Weather
The Doppler velocity pattern of a mesocyclone within a severe thunderstorm. In a storm-relative reference frame, the idealized signature is symmetric about the radar viewing direction with marked azimuthal shear across the core region between peak Doppler velocity values of opposite sign. Typical signatures consist of Doppler velocity differences of 25– 75 m s<sup>−1</sup> across core diameters of 2–8 km, with resulting azimuthal shear values of 5 × 10<sup>−3</sup> s<sup>−1</sup> to 2 × 10<sup>−2</sup> s<sup>−1</sup>.
Industry:Weather
A cyclonically rotating vortex, around 2–10 km in diameter, in a convective storm. The vorticity associated with a mesocyclone is often on the order of 10<sup>−2</sup> s<sup>−1</sup> or greater. (It should be noted that a mesocyclone is not just any cyclone on the mesoscale; it refers specifically to cyclones within convective storms. ) Mesocyclones are frequently found in conjunction with updrafts in supercells. Tornadoes sometimes form in mesocyclones. Persistent mesocyclones that have significant vertical extent are detected by Doppler radar as mesocyclone signatures. Tornado warnings may be issued when a mesocyclone signature is detected.
Industry:Weather
The study of mesoclimates; the climatology of relatively small areas that may not be climatically representative of the general region. The data used in mesoclimatology are mostly standard observations. The size of the area involved is rather indefinite and may include topographic or landscape features from a few acres to a few square miles, such as a small valley, a forest clearing, a beach, or a village site.
Industry:Weather
