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A tornadic vortex signature, abbreviated TVS, is a
Pulse-Doppler radar A pulse-Doppler radar is a radar system that determines the range to a target using pulse-timing techniques, and uses the Doppler effect of the returned signal to determine the target object's velocity. It combines the features of pulse radars and ...
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 ...
detected rotation
algorithm In mathematics and computer science, an algorithm () is a finite sequence of Rigour#Mathematics, mathematically rigorous instructions, typically used to solve a class of specific Computational problem, problems or to perform a computation. Algo ...
that indicates the likely presence of a strong mesocyclone that is in some stage of
tornadogenesis Tornadogenesis is the process by which a tornado forms. There are many types of tornadoes, varying in methods of formation. Despite ongoing scientific study and high-profile research projects such as VORTEX projects, VORTEX, tornadogenesis is a ...
. It may give meteorologists the ability to pinpoint and track the location of tornadic rotation within a larger storm, and is one component of the
National Weather Service The National Weather Service (NWS) is an Government agency, agency of the Federal government of the United States, United States federal government that is tasked with providing weather forecasts, warnings of hazardous weather, and other weathe ...
's warning operations. The tornadic vortex signature was first identified by Donald W. Burgess, Leslie R. Lemon, and Rodger A. Brown in the 1970s using experimental
Doppler radar A Doppler radar is a specialized radar that uses the Doppler effect to produce velocity data about objects at a distance. It does this by bouncing a microwave signal off a desired target and analyzing how the object's motion has altered the fre ...
at the
National Severe Storms Laboratory The National Severe Storms Laboratory (NSSL) is a National Oceanic and Atmospheric Administration (NOAA) weather research laboratory under the Office of Oceanic and Atmospheric Research. It is one of seven NOAA Research Laboratories (RLs). NSS ...
(NSSL) in
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. The National Weather Service (NWS) now uses an updated algorithm developed by NSSL, the ''tornado detection algorithm'' (TDA) based on data from its WSR-88D system of radars. NSSL also developed the ''mesocyclone detection algorithm'' (MDA).


Display

The conditions causing a TVS are often visible on the
Doppler weather radar A weather radar, also called weather surveillance radar (WSR) and Doppler weather radar, is a type of radar used to locate precipitation, calculate its motion, and estimate its type (rain, snow, hail etc.). Modern weather radars are mostly pu ...
storm relative velocity (SRV) product as adjacent inbound and outbound velocities, a signature known as a velocity couplet or "gate-to-gate" shear. In most cases, the TVS is a strong mesocyclone aloft, not an actual
tornado A tornado is a violently rotating column of air that is in contact with the surface of 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, although the ...
, although the presence of an actual tornado on the ground can occasionally be inferred based on a strong couplet in concert with a '' tornadic debris signature'' (TDS) (i.e. a "debris ball" on reflectivity or certain polarimetric characteristics), or through confirmation from storm spotters. When the algorithm is tripped, a TVS icon (typically a triangle representing a
vortex In fluid dynamics, a vortex (: vortices or vortexes) is a region in a fluid in which the flow revolves around an axis line, which may be straight or curved. Vortices form in stirred fluids, and may be observed in smoke rings, whirlpools in th ...
) and pertinent information appear. Radar analysis of the velocity couplet as well as the automated TVS are very significant to issuing tornado warnings and can suggest the strength and location of possible tornadoes. Although many tornadoes, especially the stronger ones, coincide with a TVS, many weak EF0-EF1 tornadoes can and do occur without a TVS, especially if they are not produced from an identified mesocyclone. Likewise, phenomena such as "fair-weather" waterspouts, landspouts, and
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 features ...
es, though cyclonic and occasionally damaging, do not normally produce a signature identifiable by a TVS. Rotation associated with quasi-linear convective systems (QLCSs) or
squall line A squall line, or 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 accompanied by abrupt a ...
s can trip the TVS but do so less reliably as the couplets typically are more transient, are shallower, smaller, and weaker. This rotation may be considered a
mesovortex A mesovortex is a small-scale rotational feature found in a Thunderstorm, convective storm, such as a quasi-linear convective system (QLCS, i.e. squall line), a supercell, or the eyewall of a tropical cyclone. Mesovortices range in diameter from te ...
rather than a mesocyclone but these do produce tornadoes and damaging straight-line winds.


Intensity

A TVS can be measured by intense gate to gate
wind shear Wind shear (; also written 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 ...
, which is the change of
wind speed In meteorology, wind speed, or wind flow speed, is a fundamental atmospheric quantity caused by air moving from high to low pressure, usually due to changes in temperature. Wind speed is now commonly measured with an anemometer. Wind spe ...
and/or direction across the two gates of inbound and outbound velocities. Gates are the individual pixels on the radar display. For example, if the inbound velocity is and the outbound is , then there is of gate to gate shear. The impressiveness of a TVS not only has to do with the strength of the gate to gate shear, but it also incorporates the size and depth of the TVS, and the strength of any surrounding mesocyclone, among other factors, including several vertically-polarized variables with the advent of dual-polarization. WSR-88D Distance Learning Operations Course, slide 9


See also

* Convective storm detection *
Hook echo 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. ...
* Bounded weak echo region (BWER) * Warning Decision Training Branch,
Cooperative Institute for Mesoscale Meteorological Studies The Cooperative Institute for Severe and High-Impact Weather Research and Operations (CIWRO) is one of 16 NOAA Cooperative Institutes (CIs), hosted at the University of Oklahoma. Before Oct. 1, 2021, it was known as the Cooperative Institute for ...
, Center for Analysis and Prediction of Storms,
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Notes


References

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External links


Tornado Vortex Signatures in Doppler radial velocity patterns
{{Tornado navbox Severe weather and convection Radar meteorology