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Concept
Hook echo
Summary
A hook echo is a pendant or hook-shaped weather radar signature as part of some supercell thunderstorms. It is found in the lower portions of a storm as air and precipitation flow into a mesocyclone, resulting in a curved feature of reflectivity. The echo is produced by rain, hail, or even debris being wrapped around the supercell. It is one of the classic hallmarks of tornado-producing supercells. The National Weather Service may consider the presence of a hook echo coinciding with a tornado vortex signature as sufficient to justify issuing a tornado warning.
Because of the unpredictable and potentially catastrophic nature of tornadoes, the possibility of detecting tornadoes via radar was discussed in the meteorological community in the earliest days of meteorological radar. The first association between tornadoes and the hook echo was discovered by E.M. Brooks in 1949. Brooks noted circulations with radii of approximately 8–16 km on radar. These circulations were associated with supercell thunderstorms and were dubbed “tornado cyclones” by Brooks.
The first documented association between a hook echo and a confirmed tornado occurred near Urbana-Champaign, Illinois on 9 April 1953. This event was unintentionally discovered by Illinois State Water Survey electrical engineer Donald Staggs.
Staggs was repairing and testing an experimental precipitation measurement radar unit when he noticed an unusual radar echo which was associated with a nearby thunderstorm. The unusual echo appeared to be an area of precipitation in the shape of the number six - hence the modern term “hook echo”. Staggs chose to record the echo for further analysis by meteorologists. Upon review of the unusual echo data, meteorologists F.A. Huff, H.W. Heiser, and S.G. Bigler determined that a destructive tornado had occurred in the geographical location which corresponded with the "six-shaped" echo seen on radar.
Prominent severe storm researcher Ted Fujita also documented hook echoes with various supercell thunderstorms which occurred on 9 April 1953 - the same day as the Huff et al.
Official source
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