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Concept
Heat burst
Summary
In meteorology, a heat burst is a rare atmospheric phenomenon characterized by a sudden, localized increase in air temperature near the Earth's surface. Heat bursts typically occur during night-time and are associated with decaying thunderstorms. They are also characterized by extremely dry air and are sometimes associated with very strong, even damaging, winds.
Although the phenomenon is not fully understood, the event is thought to occur when rain evaporates (virga) into a parcel of cold, dry air high in the atmosphere, making the air denser than its surroundings. The parcel descends rapidly, warming due to compression, overshoots its equilibrium level, and reaches the surface, similar to a downburst.
Recorded temperatures during heat bursts have reached well above , sometimes rising by or more within only a few minutes.
In general, heat bursts occur during the late spring and summer seasons. During these times, air-mass thunderstorms tend to generate due to daytime heating and lose their main energy during the evening hours. Due to the potential temperature increase, heat bursts normally occur at night, though they have also been recorded during the daytime. Heat bursts can vary widely in duration, from a couple of minutes to several hours. The phenomenon is usually accompanied by strong gusty winds, extreme temperature changes, and an extreme decrease in humidity. They may occur near the end of a weakening thunderstorm cluster. Dry air and a low-level temperature inversion may also be present during the storm.
Heat bursts are thought to be caused by a mechanism similar to that of downbursts. As the thunderstorm starts to dissipate, the layer of clouds starts to rise. After the clouds have risen, a rain-cooled layer remains. The cluster shoots a burst of unsaturated air down towards the ground. In doing so, the system loses all of its updraft-related fuel. The raindrops begin to evaporate into dry air, which reinforces the effects of the heat burst (evaporation cools the air, increasing its density).
Official source
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