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 has been included on the list for the role that tests of atomic weapons at Bikini played in shaping global culture in the second half of the 20th Century. Bikini Atoll is the first World Heritage site for the Marshall Islands.