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A mesocyclone is a vortex of air, about 2 to 10 km in diameter (the mesoscale of meteorology), inside a convective storm. That is, it is air that rises and rotates around a vertical axis, usually in the same direction as low pressure systems in a given hemisphere. They are most often cyclonic, that is, related with a localized low pressure area inside a severe thunderstorm. Such storms can create strong surface winds and a lot of hail. Mesocyclones often happen together with updrafts in supercells, where tornadoes may form.
Mesocyclones are normally relatively very small in size; they lie between the synoptic scale (hundreds of kilometers) and small scale (hundreds of meters).
- "American Meteorological Society Glossary - Mesocyclone". Retrieved 2006-12-07.