A bow echo is the characteristic radar return from a

mesoscale convective system A mesoscale convective system (MCS) is a complex of thunderstorms that becomes organized on a scale larger than the individual thunderstorms but smaller than extratropical cyclones, and normally persists for several hours or more. A mesoscale con ...

that is shaped like an archer's bow. These systems can produce severe

straight-line winds In meteorology, a downburst is a strong downward and outward gushing wind system that emanates from a point source above and blows radially, that is, in straight lines in all directions from the area of impact at surface level. Capable of pro ...

and occasionally

tornado A tornado is a violently rotating column of air that is in contact with both the surface of the Earth and a cumulonimbus cloud or, in rare cases, the base of a cumulus cloud. It is often referred to as a twister, whirlwind or cyclone, alt ...

es, causing major damage. They can also become

derecho A ''derecho'' (, from es, derecho, link=no , 'straight') is a widespread, long-lived, straight-line wind storm that is associated with a fast-moving group of severe thunderstorms known as a mesoscale convective system. Derechos can cause hurri ...

s or form

Line echo wave pattern A line echo wave pattern (LEWP) is a weather radar formation in which a single line of thunderstorms presenting multiple bow echoes forms south (or equatorward) of a mesoscale low-pressure area with a rotating "head". LEWP often are associated w ...

(LEWP).

Research

The term "bow echo" was first used by Theodore Fujita in his May 1978 paper "Manual of Downburst Identification for Project NIMROD." 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

supercell A supercell is a thunderstorm characterized by the presence of a mesocyclone: a deep, persistently rotating updraft. Due to this, these storms are sometimes referred to as rotating thunderstorms. Of the four classifications of thunderstorms ( ...

s. Researchers determined that bow echoes were most likely to occur in weakly organized cells. A Midwest Bow Echo Workshop was held in 2007, at which meteorologists gathered to share their research to better understand bow echoes.

Formation

A bow echo is associated with

squall line A squall line, or more accurately a quasi-linear convective system (QLCS), is a line of thunderstorms, often forming along or ahead of a cold front. In the early 20th century, the term was used as a synonym for cold front (which often are accom ...

s or lines of convective

thunderstorms A thunderstorm, also known as an electrical storm or a lightning storm, is a storm characterized by the presence of lightning and its acoustic effect on the Earth's atmosphere, known as thunder. Relatively weak thunderstorms are somet ...

. 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 strong

wind shear Wind shear (or windshear), sometimes referred to as wind gradient, is a difference in wind speed and/or direction over a relatively short distance in the atmosphere. Atmospheric wind shear is normally described as either vertical or horizont ...

exists in the lower 2 to 3 km of the

atmosphere An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A ...

. 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.MetEd Registration Page
/ref> Especially strong bow echoes that cause devastating damage all along the width of the storm are often called

Rear inflow jet

The formation of a bow echo requires a strong elevated

rear inflow jet The rear-inflow jet is a component of bow echoes in a mesoscale convective system that aids in creating a stronger cold pool and downdraft. The jet forms as a response to a convective circulation having upshear tilt and horizontal pressure gradien ...

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

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.AMS Glossary
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. As the life of the storm increases, the

Coriolis force In physics, the Coriolis force is an inertial or fictitious force that acts on objects in motion within a frame of reference that rotates with respect to an inertial frame. In a reference frame with clockwise rotation, the force acts to the ...

acts to intensify the cyclonic vortex and weaken the anticyclonic vortex. The system then develops an asymmetric comma-shaped echo. Some embedded

es or

gustnado A gustnado is a brief, shallow surface-based vortex which forms within the downburst emanating from a thunderstorm. The name is a portmanteau by elision of "gust front tornado", as gustnadoes form due to non-tornadic straight-line wind featur ...

es develop within these vortices. Bow echo diagram

Strongest winds

Damaging

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

, wind speeds can reach up to or exceed 100 mph (160 km/h) and can produce a damage path extending for hundreds of miles. 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

line echo wave pattern A line echo wave pattern (LEWP) is a weather radar formation in which a single line of thunderstorms presenting multiple bow echoes forms south (or equatorward) of a mesoscale low-pressure area with a rotating "head". LEWP often are associated w ...

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.

Notable bow echo storms

In 1674, the city of

Utrecht Utrecht ( , , ) is the fourth-largest city and a municipality of the Netherlands, capital and most populous city of the province of Utrecht. It is located in the eastern corner of the Randstad conurbation, in the very centre of mainland Net ...

in the

Netherlands ) , anthem = ( en, "William of Nassau") , image_map = , map_caption = , subdivision_type = Sovereign state , subdivision_name = Kingdom of the Netherlands , established_title = Before independence , established_date = Spanish Netherl ...

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

Europe Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a Continent#Subcontinents, subcontinent of Eurasia ...

References

External links

Manual of downburst identification for Project NIMROD
(NASA Technical Reports Server) (May 1978)
The Structure and Evolution of Squall Line and Bow Echo Convective Systems
(NWS)

(SPC)
What Creates a Bow Echo?

Glossary of Meteorology

Midwest Bow Echo Workshop

The Bow Echo and MCV Experiment: Observations and Opportunities
(''BAMS'')
The Bow Echo: Observations, Numerical Simulations, and Severe Weather Detection Methods
(''WAF'')

{{DEFAULTSORT:Bow Echo Radar meteorology Storm Severe weather and convection Weather hazards ja:気象レーダー#ボウエコー