A mesovortex is a small-scale

rotation Rotation or rotational/rotary motion is the circular movement of an object around a central line, known as an ''axis of rotation''. A plane figure can rotate in either a clockwise or counterclockwise sense around a perpendicular axis intersect ...

al feature found in a convective storm, such as a quasi-linear convective system (QLCS, i.e.

squall line A squall line, or quasi-linear convective system (QLCS), is a line of thunderstorms, often forming along or ahead of a cold front. In the early 20th century, the term was used as a synonym for cold front (which often are accompanied by abrupt a ...

), a

supercell A supercell is a thunderstorm characterized by the presence of a mesocyclone, a deep, persistently rotating updraft. Due to this, these storms are sometimes referred to as rotating thunderstorms. Of the four classifications of thunderstorms (su ...

, or the eyewall of a

tropical cyclone A tropical cyclone is a rapidly rotating storm system with a low-pressure area, a closed low-level atmospheric circulation, strong winds, and a spiral arrangement of thunderstorms that produce heavy rain and squalls. Depending on its locat ...

. Mesovortices range in diameter from tens of miles to a mile or less and can be immensely intense.

Eyewall mesovortex

An ''eyewall mesovortex'' is a small-scale rotational feature found in an eyewall of an intense tropical cyclone. Eyewall mesovortices are similar, in principle, to small "suction vortices" often observed in multiple-vortex tornadoes. In these vortices, wind speed can be up to 10% higher than in the rest of the eyewall. Eyewall mesovortices are most common during periods of intensification in tropical cyclones. 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

tornado A tornado is a violently rotating column of air that is in contact with the surface of Earth and a cumulonimbus cloud or, in rare cases, the base of a cumulus cloud. It is often referred to as a twister, whirlwind or cyclone, although the ...

es 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 Hurricane Hugo was a powerful tropical cyclone that inflicted widespread destruction across the northeastern Caribbean and the Southeastern United States in September 1989. The eleventh tropical cyclone, eighth Tropical cyclone naming, named st ...

, Hunter NOAA42 accidentally flew through an eyewall mesovortex measuring and experienced crippling

G-force The g-force or gravitational force equivalent is a Specific force, mass-specific force (force per unit mass), expressed in Unit of measurement, units of standard gravity (symbol ''g'' or ''g''0, not to be confused with "g", the symbol for ...

s 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 The Lockheed WP-3D Orion is a highly modified P-3 Orion used by the Aircraft Operations Center division of the National Oceanic and Atmospheric Administration (NOAA). The aircraft are operated by officers of the NOAA Commissioned Officer Corps. O ...

was only designed for a maximum of +3.5Gs and −1G.

Mesocyclone

A ''mesocyclone'' is a type of mesovortex, approximately in diameter (the mesoscale of meteorology), within a

convective Convection is single or multiphase fluid flow that occurs spontaneously through the combined effects of material property heterogeneity and body forces on a fluid, most commonly density and gravity (see buoyancy). When the cause of the convec ...

storm A storm is any disturbed state of the natural environment or the atmosphere of an astronomical body. It may be marked by significant disruptions to normal conditions such as strong wind, tornadoes, hail, thunder and lightning (a thunderstor ...

. Mesocyclones are 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 associated with a localized low-pressure region within a

severe thunderstorm A thunderstorm, also known as an electrical storm or a lightning storm, is a storm characterized by the presence of lightning and its acoustics, acoustic effect on the Earth's atmosphere, known as thunder. Relatively weak thunderstorm ...

. Mesocyclones are believed to form when strong changes of wind speed and/or direction with height ("

wind shear Wind shear (; also written windshear), sometimes referred to as wind gradient, is a difference in wind speed and/or direction over a relatively short distance in the atmosphere. Atmospheric wind shear is normally described as either vertical ...

") sets parts of the lower part of the atmosphere spinning in invisible tube-like rolls. The convective updraft of a thunderstorm is then thought to draw up this spinning air, tilting the air's axis of rotation upward (from parallel to the ground to perpendicular) and causing the entire updraft to rotate as a vertical column. Mesocyclones are normally relatively localized: they lie between the synoptic scale (hundreds of kilometers) and small scale (hundreds of meters). Radar imagery is used to identify these features.

Mesoscale convective vortex

A ''mesoscale convective vortex'' (MCV) is a low-pressure center ( mesolow) within a

mesoscale convective system A mesoscale convective system (MCS) is a complex of thunderstorms that becomes organized on a scale larger than the individual thunderstorms but smaller than extratropical cyclones, and normally persists for several hours or more. A mesoscale conv ...

(MCS) that pulls winds into a circling pattern, or vortex. With a core only wide and deep, an MCV is often overlooked in standard surface observations. They have most often been detected on

radar Radar is a system that uses radio waves to determine the distance ('' ranging''), direction ( azimuth and elevation angles), and radial velocity of objects relative to the site. It is a radiodetermination method used to detect and track ...

and

satellite A satellite or an artificial satellite is an object, typically a spacecraft, placed into orbit around a celestial body. They have a variety of uses, including communication relay, weather forecasting, navigation ( GPS), broadcasting, scient ...

, particularly with the higher resolution and sensitivity of WSR-88D, but with the advent of mesonets, these mesoscale features can also be detected in

surface analysis Surface weather analysis is a special type of weather map that provides a view of weather elements over a geographical area at a specified time based on information from ground-based weather stations. Weather maps are created by plotting or tra ...

. 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 A thunderstorm, also known as an electrical storm or a lightning storm, is a storm characterized by the presence of lightning and its acoustics, acoustic effect on the Earth's atmosphere, known as thunder. Relatively weak thunderstorm ...

formation. Associated low-level boundaries left behind can themselves cause

convergence Convergence may refer to: Arts and media Literature *''Convergence'' (book series), edited by Ruth Nanda Anshen *Convergence (comics), "Convergence" (comics), two separate story lines published by DC Comics: **A four-part crossover storyline that ...

and

vorticity In continuum mechanics, vorticity is a pseudovector (or axial vector) field that describes the local spinning motion of a continuum near some point (the tendency of something to rotate), as would be seen by an observer located at that point an ...

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 The Gulf of Mexico () is an oceanic basin and a marginal sea of the Atlantic Ocean, mostly surrounded by the North American continent. It is bounded on the northeast, north, and northwest by the Gulf Coast of the United States; on the southw ...

, 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 Tornadogenesis is the process by which a tornado forms. There are many types of tornadoes, varying in methods of formation. Despite ongoing scientific study and high-profile research projects such as VORTEX projects, VORTEX, tornadogenesis is a ...

. 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 Carbondale is a city in Jackson County, Illinois, United States, within the Southern Illinois region informally known as "Little Egypt". As of the 2020 United States census, 2020 census, the city had a population of 25,083, making it the most po ...

References

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