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.
Part of the Marshall Islands are a part of the US. (The islands of Bikini and Enewetak use to be US nuclear test sites.) Part of the Marshall Islands are a part of the US. (The islands of Bikini and Enewetak use to be US nuclear test sites.)