1.2.4.2.3. Evaporative cooling, virga and downbursts

  • 10 months ago
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  • Author: SW101

[ADVANCED] x.5. Heat burst

A heat burst is a special, very rare type of downburst characterized by a rapid rise in temperature, in addition to strong to severe straight line winds. Heat bursts typically occur in evening or night hours and only in a very particular set of conditions. Precipitation must start from a very high altitude and fall through a very dry airmass, evaporating completely as it falls through it. As the rain evaporates the air evaporatively cools, accelerating towards the ground and building up momentum. As the rain evaporates completely, the cooling stops and the descending cooled air begins warming adiabatically. As it descends and warms it passes the altitude where the surrounding air temperature is the same – the equilbirium level. If the descending air has sufficient momentum it reaches all the way to the ground, while warming above the temperature of surrounding air – producing a heat burst.

The air in a heat burst is not only very warm, but also exceedingly dry, desiccating the ground and plants. It can persist over an area for several hours before cooling.