The bounded weak echo region, also known as a BWER or a vault, is a

radar Radar is a system that uses radio waves to determine the distance ('' ranging''), direction ( azimuth and elevation angles), and radial velocity of objects relative to the site. It is a radiodetermination method used to detect and track ...

signature within a

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

characterized by a local minimum in radar

reflectivity The reflectance of the surface of a material is its effectiveness in Reflection (physics), reflecting radiant energy. It is the fraction of incident electromagnetic power that is reflected at the boundary. Reflectance is a component of the respon ...

at low levels which extends upward into, and is surrounded by higher reflectivities aloft, forming a kind of dome of weak echoes. This feature is associated with a strong

updraft In meteorology, an updraft (British English: ''up-draught'') is a small-scale air current, current of rising air, often within a cloud. Overview Vertical drafts, known as updrafts or downdrafts, are localized regions of warm or cool air that mov ...

and is almost always found in the inflow region of a thunderstorm: it cannot be seen visually. The BWER has been noted on radar imagery of severe thunderstorms since 1973 and has a

lightning Lightning is a natural phenomenon consisting of electrostatic discharges occurring through the atmosphere between two electrically charged regions. One or both regions are within the atmosphere, with the second region sometimes occurring on ...

detection system equivalent known as a ''lightning hole''.Martin J. Murphy and Nicholas W. S. Demetriades
An Analysis of Lightning Holes in a DFW Supercell Storm Using Total Lightning and Radar Information.
Retrieved on 2008-01-08.

Description and attributes

The BWER is a nearly vertical channel of weak radar echo, surrounded on the sides and top by significantly stronger echoes. The BWER, sometimes called a vault, is related to the strong updraft in a severe convective storm that carries newly formed atmospheric particulates, called

hydrometeor In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls from clouds due to gravitational pull. The main forms of precipitation include drizzle, rain, rain and snow mixed ("sleet" in Commonwealth ...

s, to high levels before they can grow to radar-detectable sizes. BWERs are typically found at mid-levels of convective storms, to above the ground, and are a few kilometers in horizontal diameter. Identifying the location of the updraft region is important because it is linked to locations where

severe weather Severe weather is any dangerous meteorological phenomenon with the potential to cause damage, serious social disruption, or loss of human life. These vary depending on the latitude, altitude, topography, and atmospheric conditions. High ...

normally occurs. The presence of a BWER has been part of a method to diagnose thunderstorm strength as part of the

Lemon technique The Lemon technique is a method used by meteorologists using weather radar to determine the relative strength of thunderstorm cells in a vertically sheared environment. It is named for Leslie R. Lemon, the co-creator of the current conceptual mod ...

since 1977.Leslie R. Lemon. New severe thunderstorm radar identification techniques and warning criteria: a preliminary report. Techniques Development Unit,

National Severe Storms Forecast Center The Storm Prediction Center (SPC) is a US government agency that is part of the National Centers for Environmental Prediction (NCEP), operating under the control of the National Weather Service (NWS), which in turn is part of the National Oceani ...

, Kansas City, Missouri, July 1977. The updraft strength within the BWER supports the growth of large

hail Hail is a form of solid Precipitation (meteorology), precipitation. It is distinct from ice pellets (American English "sleet"), though the two are often confused. It consists of balls or irregular lumps of ice, each of which is called a hailsto ...

stones just above the vault, which is displaced slightly into the direction of motion of the parent

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 (su ...

storm.

Detection

The bounded weak echo region (BWER) is a region of low radar reflectivity bounded above by an area of higher radar reflectivity which shows evidence of a strong updraft within mesocyclones. Radar analysts have recognized this phenomenon since at least 1973, using different elevation scans. Methods of objectively corroborating that a BWER is associated with a

mesocyclone A mesocyclone is a meso-gamma mesoscale (or storm scale) region of rotation ( vortex), typically around in diameter, most often noticed on radar within thunderstorms. In the Northern Hemisphere, it is usually located in the right rear flank ( ...

involve using a

weather radar A weather radar, also called weather surveillance radar (WSR) and Doppler weather radar, is a type of radar used to locate precipitation (meteorology), precipitation, calculate its motion, and estimate its type (rain, snow, hail etc.). Modern w ...

with the

Doppler effect The Doppler effect (also Doppler shift) is the change in the frequency of a wave in relation to an observer who is moving relative to the source of the wave. The ''Doppler effect'' is named after the physicist Christian Doppler, who described ...

to obtain the precipitation velocities. This have been available operationally in

United States The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...

since 1997 with the

NEXRAD NEXRAD or Nexrad (Next-Generation Radar) is a network of 159 high-resolution S-band pulse-Doppler radar, Doppler weather radars operated by the National Weather Service (NWS), an agency of the National Oceanic and Atmospheric Administration (NOAA) ...

network. When using the lightning detection system, lightning holes (uncovered in 2004) correspond to where a BWER would be seen on radar. A cross-section of the three-dimensional reflectivity of a thunderstorm shows the vault better. Algorithms were developed by the J.S. Marshall Radar Observatory of

McGill University McGill University (French: Université McGill) is an English-language public research university in Montreal, Quebec, Canada. Founded in 1821 by royal charter,Frost, Stanley Brice. ''McGill University, Vol. I. For the Advancement of Learning, ...

Canada Canada is a country in North America. Its Provinces and territories of Canada, ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, making it the world's List of coun ...

to locate the overhang region in a thunderstorm by the late 1980s. Its radar uses 24 angles, giving it good vertical resolution. In the United States, fewer scanning angles are made within the WSR-88D radar, which makes it more difficult to detect the overhang. Once the overhang is located, it is possible to make a cross-section to view if it is related with a BWER. However, since 1997, algorithms have been developed by the National Weather Service to determine regions of reflectivity gradient in three dimensions and the presence of BWER in convection. The development of a pronounced BWER can lead to tropical cyclone-like radar signatures over land when located with a low angle plan position indicator (PPI).David M. Roth
MCS with Eye - July 21, 2003.
Retrieved on 2008-01-08. In the lightning detection system, lightning holes (uncovered in 2004) correspond to locations where a BWER would appear on radar.

References

External links

North Carolina "Tornadocane" from 1999 - SPC

{{good article Severe weather and convection Radar meteorology

Description and attributes

Detection

See also

References

External links