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.
Bikini Atoll is one of the 29 atolls and five islands that compose the Marshall Islands. These atolls of the Marshalls are scattered over 357,000 square miles of a lonely part of the world located north of the equator in the Pacific Ocean.