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Bow echo

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Radar image of a bow echo crossingKansas Cityat 2:14 AM on 2 May 2008 (NWS Kansas City)

Abow echois the characteristic radar return from amesoscale convective systemthat is shaped like anarcher's bow.These systems can produce severestraight-line windsand occasionallytornadoes,causing major damage. They can also becomederechosor formLine echo wave pattern(LEWP).

Research[edit]

The term "bow echo" was first used byTheodore Fujitain his May 1978 paper "Manual of Downburst Identification for Project NIMROD."[1]In 2004, research was done to better anticipate the formation of bow echoes, specifically the formation of bow echoes from weakly organized squall lines andsupercells.Researchers determined that bow echoes were most likely to occur in weakly organized cells.[2]A Midwest Bow Echo Workshop was held in 2007, at which meteorologists gathered to share their research to better understand bow echoes.[3]

Formation[edit]

A bow echo is associated withsquall linesor lines of convectivethunderstorms.These echoes can range in size from 20 to 200 km, and have a life span of 3 to 6 hours. Bow echoes tend to develop when moderate to strongwind shearexists in the lower 2 to 3 km of theatmosphere.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.[4]Especially strong bow echoes that cause devastating damage all along the width of the storm are often calledderechos.

Rear inflow jet[edit]

The formation of a bow echo requires a strong elevatedrear inflow jetat 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, generatingstraight-line winds.[4]

Book end vortices[edit]

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.[5]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.[4]As the life of the storm increases, theCoriolis forceacts to intensify thecyclonicvortex and weaken theanticyclonicvortex. The system then develops an asymmetric comma-shaped echo.[4][5]Some embeddedtornadoesorgustnadoesdevelop within these vortices.

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 fordownbursts.Arrows indicate wind flow relative to the storm. Note regions ofcyclonicrotation (C) andanticyclonicrotation (A); both regions, especially C, are capable of supporting tornado development in some cases.

Strongest winds[edit]

A bow echo west of the Chicago area

Damagingstraight-line windsoften 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 aderecho,wind speeds can reach up to or exceed 100 mph (160 km/h) and can produce a damage path extending for hundreds of miles.[6]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 aline echo wave patterncreate 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.[7]

Notable bow echo storms[edit]

In 1674, the city ofUtrechtin theNetherlandswas 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 ofEurope.[8][9]

In the2014 Pentecost weekend storms in Europe,a violent bow echo moved across theRhine-Ruhrmetropolitan region,[10]causing 6 fatalities and an estimated 650 million euros in damages.[11]

See also[edit]

References[edit]

  1. ^Bow Echo Prototype
  2. ^Klimowski, Brian A.; Mark R. Hjelmfelt; Matthew J. Bunkers (August 2004)."Radar Observations of the Early Evolution of Bow Echoes".Weather and Forecasting.19(4): 727–734.Bibcode:2004WtFor..19..727K.doi:10.1175/1520-0434(2004)019<0727:ROOTEE>2.0.CO;2.
  3. ^Midwest Bow Echo Workshop
  4. ^abcdMetEd Registration Page
  5. ^abAMS GlossaryArchived19 April 2007 at theWayback Machine
  6. ^"Questions and Answers about Damaging Winds: Basics".Archived fromthe originalon 28 May 2012.Retrieved23 April2007.
  7. ^Zhao et al. 2014:http://onlinelibrary.wiley /doi/10.1002/met.1455/abstract
  8. ^"Strange storm broke the whole city in 1674".
  9. ^Van Der Schrier, Gerard; Groenland, Rob (2017)."A reconstruction of 1 August 1674 thunderstorms over the Low Countries".Natural Hazards and Earth System Sciences.17(2): 157–170.Bibcode:2017NHESS..17..157V.doi:10.5194/nhess-17-157-2017.
  10. ^"Radar Standard vom 09.06.2014, 20:10 Uhr - Nordrhein-Westfalen".Kachelmannwetter - Jetzt Lesezeichen setzen(in German).Retrieved14 January2023.
  11. ^"Versicherer: NRW-Unwetter" Ela "kostet 650 Millionen".Der Spiegel(in German). 2 July 2014.ISSN2195-1349.Retrieved14 January2023.

External links[edit]

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