Tornadic vortex signature

From Glossary of Meteorology

tornadic vortex signature

(Abbreviated TVS.) The Doppler velocity signature of a tornado or of an incipient tornado-like circulation aloft.

As the signature occurs when the radar beam is wider than the vortex, the measured Doppler velocities are weaker than the rotational velocities within the vortex and the apparent core diameter is larger than that of the vortex. The signature, which may extend throughout a considerable vertical depth, is ideally characterized by extreme Doppler velocity values of opposite sign separated in azimuth by the equivalent of one beamwidth. However, since most radars display and record Doppler velocity values at discrete azimuthal intervals, the extreme Doppler velocity values are usually at azimuthally adjacent positions that are roughly one beamwidth apart. If the centers of the radar beam and the vortex coincide, the signature includes a zero Doppler velocity value that separates the extreme values.