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Temperature Inversion and its Affects

Condition in which the temperature of the atmosphere increases with altitude in contrast to the

normal decrease with altitude. When temperature inversion occurs, cold air underlies warmer air athigher altitudes. Temperature inversion may occur during the passage of a cold front or result from

the invasion of sea air by a cooler onshore breeze. Overnight radiative cooling of surface air oftenresults in a nocturnal temperature inversion that is dissipated after sunrise by the warming of airnear the ground. A more long-lived temperature inversion accompanies the dynamics of the large

high-pressure systems depicted on weather maps. Descending currents of air near the center of thehigh-pressure system produce a warming (by adiabatic compression), causing air at middle altitudesto become warmer than the surface air. Rising currents of cool air lose their buoyancy and are

thereby inhibited from rising further when they reach the warmer, less dense air in the upper layersof a temperature inversion. During a temperature inversion, air pollution released into the

atmospheres lowest layer is trapped there and can be removed only by stro ng horizontal winds.Because high-pressure systems often combine temperature inversion conditions and low wind

speeds, their long residency over an industrial area usually results in episodes of severe smog.

Inversion of temperature is a deviation from the normal change of an atmospheric property with

altitude. It almost always refers to a temperature inversion, i.e., an increase in temperature withheight, or to the layer (inversion layer) within which such an increase occurs

An inversion can lead to pollution such as smog being trapped close to the ground, with possibleadverse effects on health. An inversion can also suppress convection by acting as a cap. If this capis broken for any of several reasons, convection of any moisture present can then erupt into violentthunderstorms. Temperature inversion can notoriously result in freezing rain in cold climates.

How and why inversions occur

Under certain conditions, the normal vertical temperature gradient is inverted such that the air is

colder near the surface of the Earth. This can occur when, for example, a warmer, less-dense airmass moves over a cooler, denser air mass. This type of inversion occurs in the vicinity of warmfronts, and also in areas of oceanic upwelling such as along the California coast in the United States.With sufficient humidity in the cooler layer, fog is typically present below the inversion cap. Aninversion is also produced whenever radiation from the surface of the earth exceeds the amount of radiation received from the sun, which commonly occurs at night, or during the winter when theangle of the sun is very low in the sky. This effect is virtually confined to land regions as the oceanretains heat far longer. In the polar regions during winter, inversions are nearly always present over

land.

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A warmer air mass moving over a cooler one can shut off any convection which may be present inthe cooler air mass. This is known as a capping inversion. However, if this cap is broken, either byextreme convection overcoming the cap, or by the lifting effect of a front or a mountain range, the

sudden release of bottled-up convective energy like the bursting of a balloon can result in severethunderstorms. Such capping inversions typically precede the development of tornadoes in theMidwestern United States. In this instance, the cooler layer is actually quite warm, but is still

denser and usually cooler than the lower part of the inversion layer capping it.

Subsidence Inversion

An inversion can develop as a result of air gradually sinking over a wide area and being warmed byadiabatic compression, usually associated with subtropical high-pressure areas. A stable marine

layer may then develop over the ocean as a result. As this layer moves over progressively warmerwaters, however, turbulence within the marine layer can gradually lift the inversion layer to higheraltitudes, and eventually, even pierce it, producing thunderstorms, and under the rightcircumstances, leading to tropical cyclones. The accumulated smog and dust under the inversion

quickly colours the sky reddish.

Source(s):

Wikipedia

Infoplease