Subsidence (atmosphere)

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Subsidence above the Congo River Basin including the Congo River and some tributaries. Note the lack of clouds above the rivers due to subsidence of colder air which precludes convection, convection being the inverse process to subsidence. Source: NASA Diatermancia Cuenca del Congo.jpg
Subsidence above the Congo River Basin including the Congo River and some tributaries. Note the lack of clouds above the rivers due to subsidence of colder air which precludes convection, convection being the inverse process to subsidence. Source: NASA
Dosen barometer showing different kinds of weather, according to atmospheric pressure, being high pressure an indication of Fair weather because of atmospheric subsidence, and being rapidly diminishing pressure, a sign to a bad weather approaching. Dosen-barometer.jpg
Dosen barometer showing different kinds of weather, according to atmospheric pressure, being high pressure an indication of Fair weather because of atmospheric subsidence, and being rapidly diminishing pressure, a sign to a bad weather approaching.

Subsidence, in the Earth's atmosphere, is most commonly caused by a low temperature. As the air cools, it becomes denser and moves towards the ground, as warm air becomes less dense and moves upwards (Atmospheric convection). Subsiding air is cold and dry and raises atmospheric pressure forming a high-pressure or anticyclonic area.

Subsidence generally causes high barometric pressure as more air moves into the same space: the polar highs are areas of almost constant subsidence, as are the horse latitudes, and the areas of subsidence are the sources of much of the world's prevailing winds.

Subsidence also causes many smaller-scale weather phenomena, such as morning fog. An extreme form of subsidence is a downburst, which can result in damage similar to that produced by a tornado. A milder form of subsidence is referred to as downdraft.

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References

  1. Cloudy Congo River Basin