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It is a form of fluid instability found in thermally stratified atmospheres in which a colder fluid overlies a warmer one. When an air mass is unstable, the element of the air mass that is displaced upwards is accelerated by the pressure differential between the displaced air and the ambient air at the (higher) altitude to which it was displaced.
In unstable stratification, on the other hand, buoyancy forces cause convection. The less-dense layers rise though the denser layers above, and the denser layers sink though the less-dense layers below. Stratifications can become more or less stable if layers change density. The processes involved are important in many science and engineering ...
Classes range from 1 (most unstable) to 7 (most stable). The Turner stability class system was devised by D. B. Turner as a modification of the Pasquill stability class system. [1] The following table is used to determine the Turner stability class for a given wind speed and net solar radiation:
There are five types of air pollution dispersion models, as well as some hybrids of the five types: [1] Box model – The box model is the simplest of the model types. [2] It assumes the airshed (i.e., a given volume of atmospheric air in a geographical region) is in the shape of a box.
As a result of the latent heat that is released during water vapor condensation, moist air has a relatively lower adiabatic lapse rate than dry air. This makes moist air generally less stable than dry air (see convective available potential energy [CAPE]). The dry adiabatic lapse rate (for unsaturated air) is 3 °C (5.4 °F) per 1,000 vertical ...
Unstable areas are in yellow (slightly) and red (highly) while the stable zone is in blue. The lifted index ( LI ) is the temperature difference between the environment Te(p) and an air parcel lifted adiabatically Tp(p) at a given pressure height in the troposphere (lowest layer where most weather occurs) of the atmosphere , usually 500 hPa ( mb ).
A third source of lift is wind circulation forcing air over a physical barrier such as a mountain (orographic lift). [10] If the air is generally stable, nothing more than lenticular cap clouds will form. However, if the air becomes sufficiently moist and unstable, orographic showers or thunderstorms may appear. [18]
The air is forced up the slope and into convection; thermal forcing in an unstable situation where there is weak general circulation and diurnal warming. The mountain breezes then generate anabatic winds which also rise. dynamic forcing when air is stable lower down, and circulation is blocked by the mountain, but the air is unstable at higher ...