<P> The following types of cyclones are not identifiable in synoptic charts . </P> <P> A mesocyclone is a vortex of air, 2.0 kilometres (1.2 mi) to 10 kilometres (6.2 mi) in diameter (the mesoscale of meteorology), within a convective storm . Air rises and rotates around a vertical axis, usually in the same direction as low - pressure systems in both northern and southern hemisphere . They are most often cyclonic, that is, associated with a localized low - pressure region within a supercell . Such storms can feature strong surface winds and severe hail . Mesocyclones often occur together with updrafts in supercells, where tornadoes may form . About 1,700 mesocyclones form annually across the United States, but only half produce tornadoes . </P> <P> A tornado is a violently rotating column of air that is in contact with both the surface of the earth and a cumulonimbus cloud or, in rare cases, the base of a cumulus cloud . Also referred to as twisters, a collequial term in America, or cyclones, although the word cyclone is used in meteorology, in a wider sense, to name any closed low - pressure circulation . </P> <P> A dust devil is a strong, well - formed, and relatively long - lived whirlwind, ranging from small (half a metre wide and a few metres tall) to large (more than 10 metres wide and more than 1000 metres tall). The primary vertical motion is upward . Dust devils are usually harmless, but can on rare occasions grow large enough to pose a threat to both people and property . </P>

What is a cyclone known as in american continent
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