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A mesovortex is a small-scale feature found in a Thunderstorm, such as a quasi-linear convective system (QLCS, i.e. squall line), a supercell, or the eyewall of a tropical cyclone. Mesovortices range in diameter from tens of miles to a mile or less and can be immensely intense.
Eyewall mesovortices often exhibit unusual behavior in tropical cyclones. They usually revolve around the low pressure center, but sometimes they remain stationary. Eyewall mesovortices have even been documented to cross the eye of a storm. These phenomena have been documented observationally, experimentally, and theoretically.
Eyewall mesovortices are a significant factor in the formation of after tropical cyclone landfall. Mesovortices can spawn rotation in individual thunderstorms (a mesocyclone), which leads to tornadic activity. At landfall, friction is generated between the circulation of the tropical cyclone and land. This can allow the mesovortices to descend to the surface, causing large outbreaks of tornadoes.
On 15 September 1989, during observations for Hurricane Hugo, Hunter NOAA42 accidentally flew through an eyewall mesovortex measuring and experienced crippling of +5.8Gs and -3.7Gs. The winds ripped off the propeller de-icing boot and pushed the flight down to a perilous above sea level. The ruggedized Lockheed WP-3D Orion was only designed for a maximum of +3.5Gs and −1G.
An MCV can persist for more than 12 hours after its parent MCS has dissipated. This orphaned MCV will sometimes then become the seed of the next thunderstorm outbreak. Their remnants will often lead to an "agitated area" of increased cumulus activity that can eventually become an area of thunderstorm formation. Associated low-level Outflow boundary left behind can themselves cause Convergence zone and vorticity that can increase the level of organization and intensity of any storms that do form.
An MCV that moves into tropical waters, such as the Gulf of Mexico, can serve as the nucleus for a tropical cyclone (as in the case of Hurricane Barry in 2019, for instance). MCVs, like mesovortices, often cause an intensification of convective downburst winds and can lead to tornadogenesis. One form of MCV is the "comma head" of a line echo wave pattern (LEWP).
Example of May 2009 Mid-Mississippi Valley MCV
On Friday, May 8, 2009, a major MCV controversially dubbed an "inland hurricane" by local media moved through southern Missouri, southern Illinois, western Kentucky, and southwestern Indiana, killing at least six and injuring dozens more. Damage estimates were in the hundreds of millions. Top speeds of were reported in Carbondale, Illinois.
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