- Industry: Weather
- Number of terms: 60695
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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 resultant fetch (ocean area where waves are generated by a wind having a constant direction and speed) if a wind field is moving together with a wave field.
Industry:Weather
A mercury barometer of the fixed cistern type in which a movable scale terminating in an ivory point is used to compensate for the variations in height of the mercury in the cistern. The position of the scale is adjusted so that the ivory point just touches the mercury in the cistern.
Industry:Weather
A cloud that forms in the rising branches of mountain waves and occupies the crests of the waves. The most distinctive are the sharp-edged, lens-, or almond-shaped lenticular clouds, but a variety of stratocumulus, altocumulus, and cirrocumulus forms appear in both the main, vertically propagating waves and in the lee waves. See mountain wave, foehn cloud.
Industry:Weather
A local wind blowing through a gap between mountains, a gap wind. This term was introduced by R. S. Scorer (1952) for the surface winds blowing through the Strait of Gibraltar. When air stratification is stable, as it usually is in summer, the air tends to flow through the gap from high to low pressure, emerging as a “jet” with large standing eddies in the lee of the gap. The excess of pressure on the upwind side is attributed to a pool of cold air held up by the mountains. Similar winds occur at other gaps in mountain ranges, such as the tehuantepecer and the jochwinde, and in long channels, such as the Strait of Juan de Fuca between the Olympic Mountains of Washington and Vancouver Island, British Columbia. Compare jet-effect wind, canyon wind, mountain wind.
Industry:Weather
A nocturnal, thermally forced wind from the direction of the mountains, generated by cooling along the mountain slopes; a downvalley wind, or the nighttime downslope (katabatic) component of a mountain–plains wind system.
Industry:Weather
An atmospheric gravity wave, formed when stable air flow passes over a mountain or mountain barrier. Mountain waves are often standing or nearly so, at least to the extent that upstream environmental conditions (and diurnal forcing) are stationary. Two divisions of mountain wave are recognized, vertically propagating and trapped lee waves. Vertically propagating mountain waves over a barrier may have horizontal wavelengths of many tens of kilometers or more, usually extend upward into the lower stratosphere, and in pure form, tilt upwind with height. They can accompany foehn, chinook, or bora wind conditions. They have the capability to concentrate momentum on the lee slopes, sometimes in structures resembling a hydraulic jump, leading to occasionally violent downslope windstorms. When sufficient moisture is present in the upstream flow, vertically propagating mountain waves produce interesting cloud forms, including altocumulus standing lenticular (ACSL) and other foehn clouds. Intense waves can present a significant hazard to aviation by producing severe or even extreme clear air turbulence. Trapped lee waves generally have horizontal wavelengths of 5–35 km. They occur within or beneath a layer of high static stability and moderate wind speeds at low levels of the troposphere (the lowest 1–5 km) lying beneath a layer of low stability and strong winds in the middle and upper troposphere. These conditions are often diagnosed using a vertical profile of the Scorer parameter, a sharp decrease in midtroposphere indicating conditions favorable to trapped lee wave formation. Trapped lee waves assume the form of a series of waves running parallel to the ridges, and the crests of these waves often contain altocumulus, stratocumulus, wave clouds, or rotor clouds in parallel bands that can be very striking in satellite pictures. Because wave energy is trapped within the stable layer, these waves (and accompanying cloud bands) may dissipate only very slowly downwind, and they can continue downstream for many wavelengths spanning many tens of kilometers. Flow beneath the wave crests, occasionally made visible by rotor clouds, is often turbulent, thus presenting a significant hazard to low-level aviation. Vertically propagating mountain waves and trapped lee waves can coexist, and sometimes lee waves are incompletely trapped or “leaky,” leading to a variety of complex rotor interactions. This complexity of rotor patterns often produces interesting variations in cloud forms. As mountain waves propagate upward, the rotor's amplitude can grow to the point that the rotor “breaks,” that is, the rotor becomes convectively unstable and overturns. Wave breaking can have an important role in vertically redistributing horizontal atmospheric momentum, as it slows the atmosphere by turbulent transport of the earth's momentum upward.
Industry:Weather
The torque about a given axis exerted on or by the earth's surface due to the force associated with a difference of pressure on two sides of a mountain. For example, if the axis is the earth's polar axis and the air pressure is higher (level for level) on the west side of a mountain than on the east, there exists a mountain torque in the vicinity tending to speed up the earth's rotation. See also frictional torque.
Industry:Weather
Fog formed by orographic lifting to condensation of moist air up a mountain slope. See orographic fog.
Industry:Weather
A collection of simultaneous meteorological measurements taken and recorded in a mountainous location. The harshness of the high-mountain environment, the inaccessibility of sites, and the remoteness of these regions are special problems that have limited the availability of long-term records of mountain weather. These difficulties are compounded by the issue of representativeness of a measurement. Over flatter, simpler terrain, care is taken to place instrumentation in exposed locations where the measurement can be considered as representing a larger area. Barry (1992) defines at least three types of situations in the mountains: “summit, slope, and valley bottom apart from considerations of slope orientation; slope angle; topographic screening; and irregularities of small-scale relief. ” Thus it is very difficult; perhaps inappropriate; to claim representativeness for a single observation; and one must interpret mountain observations with great caution. Barry further states; “These factors necessitate either a very dense network of stations or some other approach to determining mountain climate. In the future; the use of ground-based and satellite remote sensors combined with intensive case studies of particular phenomena; may provide the best solution. ”
Industry:Weather
Generally, the climate of high elevations. Mountain climates are distinguished by the departure of their characteristics from those of surrounding lowlands, and the one common basis for this distinction is that of atmospheric rarefaction. Aside from this, great variety is introduced by differences in latitude, elevation, and exposure to the sun. Thus, there exists no single, clearly defined, mountain climate. The most common climatic results of high elevation are those of decreased pressure, reduced oxygen availability, decreased temperature, and increased insolation; the last two combine to produce a typical “hot sun and cold shade” condition. Precipitation is heavier on the windward side of a mountain barrier than on the leeward (orographic precipitation), and on the windward side it increases upward to the zone of maximum precipitation, then decreases again. On many tropical mountains the forest zone extends into the level of average cloud height, which causes an excessively damp climate and produces the so-called fog forest. The orography gives rise to many local winds, chief among which are the foehn, mountain and valley winds, mountain-gap winds, and downslope winds of many sorts. Great interest in mountain climate has centered in the relatively well- populated, equatorial Andes. There, four zones of elevation are delimited: tierra caliente (hot land); tierra tamplada (temperate land); tierra fria (cool land); and tierra helada (land of frost).
Industry:Weather
