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.
Kwajalein is one of the world's largest coral atolls as measured by area of enclosed water. Comprising 97 islands and islets, it has a land area of 16.4 kmÂ² (6.33 miÂ²) and surrounds one of the largest lagoons in the world, with an area of 2174 kmÂ² (839 miÂ²).