pulse storm
{{Short description|Thunderstorm that produces severe weather for short periods}}
A pulse storm is a single cell thunderstorm of substantial intensity which only produces severe weather for short periods of time. Such a storm weakens and then generates another short burst – hence "pulse". The term was coined by researchers at the National Severe Storms Laboratory in 1979 to describe a single storm cell briefly becoming severe within a cluster of multi-cellular thunderstorms, but has since been used to describe a variety of isolated and brief thunderstorms with both severe and non-severe characteristics.{{cite journal |last1=Miller |first1=Paul W. |last2=Mote |first2=Thomas L. |title=Standardizing the Definition of a “Pulse” Thunderstorm |journal=Bulletin of the American Meteorological Society |date=May 2017 |volume=98 |issue=5 |pages=905–913 |doi=10.1175/BAMS-D-16-0064.1|doi-access=free}}
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Description
Single cell thunderstorms ordinarily form in environments with low wind shear and moderate instability, with the low wind shear contributing to a short average lifespan of less than an hour.{{cite web|url=http://www.theweatherprediction.com/habyhints2/400/ |title=What is a pulse storm?|website=www.theweatherprediction.com|author=Jeff Haby|accessdate=February 20, 2020}} When the instability, calculated by convective available potential energy (CAPE), is strong, the updraft will bring a larger amount of humid air very high above ground and generate a cumulonimbus cloud with high water and ice content. When the rain content, and even hail, falls from it, they can generate damaging winds brought about by downbursts. Rarely, a weak tornado develops in association with a pulse storm as the environment is only weakly sheared, or not at all.{{cite web|url=https://forecast.weather.gov/glossary.php?letter=p|work=Glossary|publisher=US National Weather service|title=Pulse storm|accessdate=February 20, 2020}}
Life cycle
One can distinguish three stages in the evolution of a pulse storm:{{cite web|url=http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/svr/type/sngl/ev.rxml |title=Evolution of a Single Cell Storm|website=ww2010.atmos.uiuc.edu |publisher=University of Illinois|author=Departement of Atmospheric Sciences|accessdate=2020-02-19}}
- Formation: the upward current of the cell intensifies and allows the condensation of water vapor from the rising air parcel. This forms a cumulus congestus, then a cumulonimbus when ice crystals form at its apex which spreads horizontally in contact with the tropopause.
- Maturity: downdrafts are emerging. This stage is accompanied by characteristic phenomena such as lightning and thunder, showers, and gust front.
- Dissipation: the cold pool descending from the cloud extends to the Earth's surface and helps to block the feed by pushing the updraft downstream. The outflow can then serve as a trigger for other single cell or even multi-cell thunderstorms.
See also
References
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Category:Severe weather and convection
fr:Orage#Orage ordinaire et pulsatif
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