Literally, in order for a vortex to be classified as a tornado, it must be in contact with the ground and the cloud base. Weather scientists haven't found it so simple in practice, however, to classify and define tornadoes (per this essay by Doswell).
Bikini Island, 2015. Credit: Emlyn Hughes. (Phys.org)âA team of researchers from Columbia University in New York has found that all of the Marshall Islands involved in nuclear tests by the U.S. are now habitable, except for Bikini Atoll.
Prior to the first nuclear test in 1946, the 167 Bikinians living on Bikini Island were evacuated to neighbouring islands. By the time nuclear-weapon testing in the Marshall Islands was terminated in July 1958, twenty three nuclear-weapon tests had been conducted on Bikini Atoll over a 12-year period.