Mesovortices
Encyclopedia
Mesovortices are small scale rotation
al features found in convective storms, such as those found in bow echo
s, supercell thunderstorms
and the eyewall of tropical cyclone
s.
. 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 rotate 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
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.
A mesocyclone is a type of mesovortex, approximately 2 to 10 km in diameter (the mesoscale of meteorology
), within a convective
storm
.
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. Mesocyclones are believed to form when strong changes of wind speed and/or direction with height ("wind shear
") 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.
Rotation
A rotation is a circular movement of an object around a center of rotation. A three-dimensional object rotates always around an imaginary line called a rotation axis. If the axis is within the body, and passes through its center of mass the body is said to rotate upon itself, or spin. A rotation...
al features found in convective storms, such as those found in bow echo
Bow echo
A bow echo is a term describing the characteristic radar return from a mesoscale convective system that is shaped like an archer’s bow. These systems can produce severe straight-line winds and occasionally tornadoes, causing major damage.-Research:...
s, supercell thunderstorms
Supercell
A supercell is a thunderstorm that is characterized by the presence of a mesocyclone: a deep, continuously-rotating updraft. For this reason, these storms are sometimes referred to as rotating thunderstorms...
and the eyewall of tropical cyclone
Tropical cyclone
A tropical cyclone is a storm system characterized by a large low-pressure center and numerous thunderstorms that produce strong winds and heavy rain. Tropical cyclones strengthen when water evaporated from the ocean is released as the saturated air rises, resulting in condensation of water vapor...
s.
Eyewall mesovortices
Eyewall mesovortices are small scale rotational features found in the eyewalls of intense tropical cyclones. They are similar, in principle, to small "suction vortices" often observed in multiple-vortex tornadoesMultiple vortex tornado
A multiple-vortex tornado is a tornado that contains several vortices rotating around, inside of, and as part of the main vortex. These multiple vortices are somewhat similar to eyewall mesovortices found in intense tropical cyclones...
. 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 rotate 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
Tornado
A tornado is a violent, dangerous, 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. They are often referred to as a twister or a cyclone, although the word cyclone is used in meteorology in a wider...
es after tropical cyclone landfall. Mesovortices can spawn rotation in individual thunderstorms (a mesocyclone
Mesocyclone
A mesocyclone is a vortex of air, approximately 2 to 10 miles in diameter , within a convective storm....
), 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.
Mesocyclone
A mesocyclone is a type of mesovortex, approximately 2 to 10 km in diameter (the mesoscale of meteorology
Mesoscale meteorology
Mesoscale meteorology is the study of weather systems smaller than synoptic scale systems but larger than microscale and storm-scale cumulus systems. Horizontal dimensions generally range from around 5 kilometers to several hundred kilometers...
), within a convective
Convection
Convection is the movement of molecules within fluids and rheids. It cannot take place in solids, since neither bulk current flows nor significant diffusion can take place in solids....
storm
Storm
A storm is any disturbed state of an astronomical body's atmosphere, especially affecting its surface, and strongly implying severe weather...
.
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. Mesocyclones are believed to form when strong changes of wind speed and/or direction with height ("wind shear
Wind shear
Wind shear, sometimes referred to as windshear or wind gradient, is a difference in wind speed and direction over a relatively short distance in the atmosphere...
") 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
Synoptic scale meteorology
The synoptic scale in meteorology is a horizontal length scale of the order of 1000 kilometres or more. This corresponds to a horizontal scale typical of mid-latitude depressions...
(hundreds of kilometers) and small scale (hundreds of meters). Radar imagery is used to identify these features.