- Settore: 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 processes that occur as a consequence of the air being in contact with the sea surface, and that affect the dynamics and thermodynamics of the air and water boundary layers. These include 1) the exchange of momentum, heat, mechanical energy (e.g., wave energy, turbulence), and mass (water vapor, gas species, particulates, sea spray, air bubbles, etc. ); 2) the generation of surface waves; 3) the generation of turbulence; and 4) the resulting effects on the vertical profiles of wind and current.
Industry:Weather
The officially designated elevation of an airport above mean sea level, in international usage denoted by the symbol Ha. It is the elevation of the highest point on any of the runways of the airport. Compare station elevation.
Industry:Weather
Region where air masses originate and acquire their horizontal homogeneous properties of temperature and moisture. Horizontal homogeneity of the air mass is produced by prolonged contact (days to weeks) with the underlying surface. Main source regions are those in which the permanent or semipermanent anticyclones occur.
Industry:Weather
A shower that is produced by local convection within an unstable air mass; the most common type of airmass precipitation. Such showers are not associated with a front or instability line. They are most frequent within a moist air mass that is sufficiently unstable so that daytime heating at the surface can produce well-developed cumulus clouds. The extreme form of airmass shower is the airmass thunderstorm.
Industry:Weather
Any precipitation that can be attributed only to moisture and temperature distribution within an air mass when that air is not, at that location, being influenced by a front or by orographic lifting. The most common form of airmass precipitation is airmass showers; however, a moist but stable air mass may produce drizzle independent of frontal or orographic influences.
Industry:Weather
The change of characteristics of an air mass as it moves away from its region of origin. For example, maritime air at midlatitudes that originally has high humidity and cool temperatures can be modified as it blows onshore over coastal mountains, where orographic precipitation causes the air to become drier and warmer by the time it reaches the lee side of the mountains. The rate of airmass modification depends on the differences between its original characteristics and those of the new surface over which it flows.
Industry:Weather
The representation of the climate of a region by the frequency and characteristics of the air masses under which it lies; basically, a type of synoptic climatology. It is a development of the representation of the weather associated with winds of different directions (thermal wind roses, etc. ) by taking account of the source and trajectory of the air, and it gives a more dynamic picture of the climate than do monthly averages. The first detailed study was by E. Dinies (1932). Dinies gave tables of average temperature, humidity, and cloudiness in Germany associated with eight classes of air in winter and summer (Durst 1951). Similar tables have since been constructed for many parts of the world.
Industry:Weather
A system used to identify and to characterize the different air masses according to a basic scheme. A number of systems have been proposed, but the Bergeron classification has been the most widely accepted. In this system, air masses are designated first according to the thermal properties of their source regions: tropical (T); polar (P); and less frequently, arctic or antarctic (A). For characterizing the moisture distribution, air masses are distinguished as to continental (c) and maritime (m) source regions. Further classification according to whether the air is cold (k) or warm (w) relative to the surface over which it is moving indicates the low-level stability conditions of the air, the type of modification from below, and is also related to the weather occurring within the air mass. This outline of classification yields the following identifiers for air masses: cTk, cTw, mTk, mTw, cPk, cPw, mPk, mPw, cAk, mAk, mAw; the last of which is never used. H. C. Willett, in his classification, introduces further distinction between stable (s) and unstable (u) conditions in upper levels. Some authors may include equatorial (E), monsoon (M), or superior air (S) in their classifications. Others prefer to omit the arctic (A) type and describe all air masses on the basis of polar and tropical air, separated by the polar front.
Industry:Weather
In general, the theory and practice of surface synoptic chart analysis by the so- called Norwegian methods, which involve the concepts of the polar front and of the broad-scale air mass that it separates. Airmass analysis of surface charts may be said to consist of 1) determining the extent, the physical and stability properties, the movements, and the modifications of each of the air masses on the chart; 2) locating with some precision the fronts separating the air masses, and analyzing the structure and motion of the fronts; 3) analyzing wave perturbations on the fronts; and 4) describing and explaining the weather on the basis of the above factors.
Industry:Weather
