Heat burst

  • 11 months ago
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  • Author: SW101

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.

Essentially, a heat burst is very similar to a dry downburst. Airmass in heat bursts originates high in the thunderstorm. A deep, elevated layer of very dry air needs to be present. Heat bursts typically occur during the night (late night or early morning). During the night the air close to the ground cools, forming a low level temperature inversion. This additionally increases the temperature difference between heat burst airmass and surface airmass.

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.

Some remarkable heat burst events:

  • Torcy, Seine-et-Marne, France – April 29, 2012:
  • Wichita, Kansas – June 9, 2011: between 12:22 and 12:24 am temperatures rose from 29 °C to 39 °C in winds up to 80 km/h.
  • Sheppard Air Force Base, Wichita Falls, Texas – June 11, 2004: National Weather Service in Norman, Oklahoma reported a heat burst at Sheppard Air Force Base, Wichita Falls, Texas just before local midnight. Temperature abruptly rose from 28.3 °C to 34.4 °C in winds gusting up to 116 km/h. Dewpoint fell from 21.1 °C to 3.9 °C.
  • Midland, Texas – June 16, 2008: wind gusts up to 100 km/h recorded, temperature rose from 21.7 °C to 36.1 °C in minutes.
  • Emporia, Kansas – May 25, 2008: temperature increased from 21.7 °C to 32.8 °C betwen 4:44 and 5:11 am.
  • Cherokee, Oklahoma – July 11, 1909: at 3 am in the morning temperature rose to 57.8 °C, reportedly desiccating crops.

Dodatni detajli: http://www.crh.noaa.gov/oun/?n=heatburst_info