Tornado echo

From Glossary of Meteorology

tornado echo

A type of precipitation echo observed in connection with large, strong tornadoes located at relatively close ranges from a radar.

It appears on PPI displays in the form of a doughnut-shaped echo at the end of a hook echo in a supercell thunderstorm. A quasi-vertical tube having minimum radar reflectivity in the center may be observed on an RHI display or on a vertical sequence of PPI displays.