A tornado vortex signature or tornadic vortex signature, abbreviated TVS, is a Doppler weather radar detected rotation algorithm that indicates the likely presence of a strong mesocyclone that is in some stage of tornadogenesis.[1] It may give meteorologists the ability to pinpoint and track the location of tornadic rotation within a larger storm, but it is not an important feature in the National Weather Service's warning operations.
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It is often visible on the Doppler radar storm relative velocity product as side by side inbound and outbound velocities, a signature known as a velocity couplet or "gate-to-gate" shear.[2] In many cases, the TVS is a strong mesocyclone aloft, not an actual tornado, although the presence of an actual tornado on the ground can occasionally be inferred based on a strong couplet in concert with a debris cloud signature, or through confirmation from storm spotters. When the algorithm is tripped, a TVS icon and pertinent information appear.[3] 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 EF0-1 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 and gustnadoes, though cyclonic and occasionally destructive, do not normally produce a signature identifiable by a TVS.[4]
A TVS can be measured by gate to gate wind shear, which is the change of wind speed and 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 −48 knots (−88.9 km/h) knots and the outbound is 39 knots (72 km/h), then there is 87 knots (161 km/h) of gate to gate shear.[5] 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 things.[6]