View source for Earth:Bow echo

{{Short description|Mesoscale convective system shaped like a archer's bow}}
[[File:Bow Echo Kansas City.jpg|thumb|300px|Radar image of a bow echo crossing Kansas City at 2:14 AM on 2 May 2008 (NWS Kansas City)]]
A '''bow echo''' is the characteristic radar return from a [[Earth:Mesoscale convective system|mesoscale convective system]] that is shaped like an archer's bow.  These systems can produce severe straight-line winds and occasionally [[Earth:Tornado|tornado]]es, causing major damage. They can also become [[Earth:Derecho|derecho]]s or form [[Earth:Line echo wave pattern|Line echo wave pattern]] (LEWP).

==Research==

The term "bow echo" was first used by Theodore Fujita in his May 1978 paper "Manual of Downburst Identification for Project NIMROD."<ref>[http://www.spc.noaa.gov/misc/AbtDerechos/bowechoprot.htm Bow Echo Prototype<!-- Bot generated title -->]</ref>  In 2004, research was done to better anticipate the formation of bow echoes, specifically the formation of bow echoes from weakly organized squall lines and [[Earth:Supercell|supercell]]s.  Researchers determined that bow echoes were most likely to occur in weakly organized cells.<ref>{{cite journal|last=Klimowski|first=Brian A.|author2=Mark R. Hjelmfelt|author3=Matthew J. Bunkers|title=Radar Observations of the Early Evolution of Bow Echoes|journal=Weather and Forecasting|date=August 2004|volume=19|issue=4|pages=727–734|doi=10.1175/1520-0434(2004)019<0727:ROOTEE>2.0.CO;2|bibcode = 2004WtFor..19..727K |url=https://zenodo.org/record/1234659|doi-access=free}}</ref>  A Midwest Bow Echo Workshop was held in 2007, at which meteorologists gathered to share their research to better understand bow echoes.<ref>[http://www.crh.noaa.gov/lmk/?n=bowechoworkshop Midwest Bow Echo Workshop<!-- Bot generated title -->]</ref>

==Formation==

A bow echo is associated with [[Earth:Squall line|squall line]]s or lines of convective thunderstorms.  These echoes can range in size from 20 to 200&nbsp;km, and have a life span of 3 to 6 hours.  Bow echoes tend to develop when moderate to strong [[Physics:Wind shear|wind shear]] exists in the lower 2 to 3&nbsp;km of the [[Astronomy:Atmosphere|atmosphere]].  While similar to squall lines, bow echoes are smaller in scale and are moved by the wind inside them. They tend to push outward and after time die out. A bow echo also lowers the chance of a tornado being formed in the storm itself.  The "bow shaped" echo is a result of focusing of the strong flow at the rear of the system.<ref name="MetEd Registration Page">[http://www.meted.ucar.edu/mesoprim/severe2/ MetEd Registration Page<!-- Bot generated title -->]</ref>  Especially strong bow echoes that cause devastating damage all along the width of the storm are often called [[Earth:Derecho|derecho]]s.

===Rear inflow jet===

The formation of a bow echo requires a strong elevated rear inflow jet at mid-levels.  The strength of the cold pool and mesohigh at the surface as well as warmer temperatures aloft due to convection works to create a mesolow at mid-levels which strengthens the jet.  Upon reaching the edge of the convection the jet descends and spreads along the surface, generating straight-line winds.<ref name="MetEd Registration Page" />

===Book end vortices===

After the rear inflow jet has bowed the storm system, book end or line end vortices develop on either side of the jet.  These vortices are similar in strength.<ref name="AMS Glossary">[http://amsglossary.allenpress.com/glossary/search?id=bow-echo1 AMS Glossary<!-- Bot generated title -->] {{webarchive|url=https://web.archive.org/web/20070419135122/http://amsglossary.allenpress.com/glossary/search?id=bow-echo1 |date=19 April 2007 }}</ref>  Due to the small size of the bow echo, the vortices help enhance the mid-level flow between them, which strengthens the rear inflow jet.  The surface winds increase from the descending jet.<ref name="MetEd Registration Page" />  As the life of the storm increases, the [[Physics:Coriolis force|Coriolis force]] acts to intensify the cyclonic vortex and weaken the anticyclonic vortex.  The system then develops an asymmetric comma-shaped echo.<ref name="MetEd Registration Page" /><ref name="AMS Glossary"/>  Some embedded [[Earth:Tornado|tornado]]es or [[Earth:Gustnado|gustnado]]es develop within these vortices.

[[File:Bow echo diagram.svg|frame|center|Typical evolution of a thunderstorm radar echo (a) into a bow echo (b, c) and into a comma echo (d). Dashed line indicates axis of greatest potential for [[Earth:Downburst|downburst]]s. Arrows indicate wind flow relative to the storm. Note regions of cyclonic rotation (C) and anticyclonic rotation (A); both regions, especially C, are capable of supporting tornado development in some cases.]]

==Strongest winds==

[[File:Bow echo chicago.jpg|thumbnail|A bow echo west of the Chicago area]]

Damaging straight-line winds often occur near the center of a bow echo. Damage from all severe thunderstorm winds accounts for half of all severe reports in the lower 48 states of the US, and is more common than damage from tornadoes. In a type of long-lived and powerful bow echo known as a [[Earth:Derecho|derecho]], wind speeds can reach up to or exceed 100&nbsp;mph (160&nbsp;km/h) and can produce a damage path extending for hundreds of miles.<ref>{{Cite web |url=http://www.nssl.noaa.gov/primer/wind/wind_basics.html |title=Questions and Answers about Damaging Winds: Basics<!-- Bot generated title --> |access-date=23 April 2007 |archive-date=28 May 2012 |archive-url=https://web.archive.org/web/20120528080037/http://www.nssl.noaa.gov/primer/wind/wind_basics.html |url-status=dead }}</ref>  Bow echoes are capable of producing straight-line winds that are just as strong as many tornadoes.  Indeed, a strong bow echo will produce more widespread and intense damage than the majority of tornadoes. Also, bow echoes in the form of a [[Earth:Line echo wave pattern|line echo wave pattern]] create a favorable environment for tornadoes to form.

The semiarid climate and rugged terrain in the interior west of the United States do not favour the development of bow echoes. However, on 21 April 2011, a bow echo associated with a fast-moving mid-tropospheric perturbation formed across the Great Salt Lake (GSL) in Utah, producing damaging winds along its path.<ref>Zhao et al. 2014: http://onlinelibrary.wiley.com/doi/10.1002/met.1455/abstract</ref>

==Notable bow echo storms==

In 1674, the city of Utrecht in the Netherlands was devastated by a storm now thought to have been a bow echo storm.  Some of the damage to the city is still visible, and severe storm activity was recorded across other areas of [[Earth:Europe|Europe]].<ref>{{Cite web|url=https://scienceinfo.net/strange-storm-broke-the-whole-city-in-1674.html|title = Strange storm broke the whole city in 1674}}</ref><ref>{{Cite journal|url=https://nhess.copernicus.org/articles/17/157/2017/|doi = 10.5194/nhess-17-157-2017|title = A reconstruction of 1 August 1674 thunderstorms over the Low Countries|year = 2017|last1 = Van Der Schrier|first1 = Gerard|last2 = Groenland|first2 = Rob|journal = Natural Hazards and Earth System Sciences|volume = 17|issue = 2|pages = 157–170|bibcode = 2017NHESS..17..157V|doi-access = free}}</ref>

== See also ==
* [[Earth:Convective storm detection|Convective storm detection]]
* [[Earth:Derecho|Derecho]]
* [[Earth:Gustnado|Gustnado]]
* [[Earth:Hook echo|Hook echo]]
* [[Earth:Mesoscale convective system|Mesoscale convective system]]
* [[Earth:Outflow boundary|Outflow boundary]]
* [[Earth:Rear-inflow jet|Rear-inflow jet]]
* [[Earth:Tornado|Tornado]]

==References==
{{reflist}}

== External links ==
* [http://naca.larc.nasa.gov/search.jsp?R=19780022828&qs=N%3D4294129240%2B4294956360%2B4294809542 Manual of downburst identification for Project NIMROD]{{dead link|date=June 2021|bot=medic}}{{cbignore|bot=medic}} (NASA Technical Reports Server) (May 1978)
* [http://www.crh.noaa.gov/lmk/soo/docu/bowecho.php The Structure and Evolution of Squall Line and Bow Echo Convective Systems] (NWS)
* [http://www.spc.noaa.gov/misc/AbtDerechos/bowechoprot.htm Bow Echo Prototype] (SPC)
* [http://www.theweatherprediction.com/habyhints2/386/ What Creates a Bow Echo?]
* [https://web.archive.org/web/20070419135122/http://amsglossary.allenpress.com/glossary/search?id=bow-echo1 Glossary of Meteorology]
* [http://www.crh.noaa.gov/lmk/?n=bowechoworkshop Midwest Bow Echo Workshop]
* [http://ams.allenpress.com/perlserv/?request=get-document&doi=10.1175%2FBAMS-85-8-1075 The Bow Echo and MCV Experiment: Observations and Opportunities] (''BAMS'')
* [http://ams.allenpress.com/perlserv/?request=get-abstract&doi=10.1175%2F1520-0434(1995)010%3C0203%3ATBEONS%3E2.0.CO%3B2 The Bow Echo: Observations, Numerical Simulations, and Severe Weather Detection Methods] (''WAF'')
* [https://scienceinfo.net/strange-storm-broke-the-whole-city-in-1674.html Strange storm broke the whole city in 1674]

{{DEFAULTSORT:Bow Echo}}
[[Category:Radar meteorology]]
[[Category:Storm]]
[[Category:Severe weather and convection]]
[[Category:Weather hazards]]

ja:気象レーダー#ボウエコー

{{Sourceattribution|Bow echo}}