A mesohigh (sometimes called a "bubble high") is a mesoscale

high-pressure area A high-pressure area, high, or anticyclone, is an area near the surface of a planet where the atmospheric pressure is greater than the pressure in the surrounding regions. Highs are middle-scale meteorological features that result from interpl ...

that forms beneath

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

. While not always the case, it is usually associated with 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 con ...

. In the early stages of research on the subject, the mesohigh was often referred to as a "thunderstorm high".

Formation

A mesohigh forms underneath the

downdraft In meteorology, an updraft is a small-scale current of rising air, often within a cloud. Overview Localized regions of warm or cool air will exhibit vertical movement. A mass of warm air will typically be less dense than the surrounding region, ...

in a

squall line A squall line, or more accurately a 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 accompa ...

and is associated with the

cold pool In atmospheric science, a cold pool (CP) is a cold pocket of dense air that forms when rain evaporates during intense precipitation e.g. underneath a thunderstorm cloud. Typically, CPs spread at 10 m/s and last 2–3 hours. Characteristics C ...

of a thunderstorm. It is largely formed by

hydrostatic Fluid statics or hydrostatics is the branch of fluid mechanics that studies the condition of the equilibrium of a floating body and submerged body "fluids at hydrostatic equilibrium and the pressure in a fluid, or exerted by a fluid, on an imme ...

phenomenon, specifically the

evaporation Evaporation is a type of vaporization that occurs on the surface of a liquid as it changes into the gas phase. High concentration of the evaporating substance in the surrounding gas significantly slows down evaporation, such as when humidi ...

of falling

precipitation In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls under gravitational pull from clouds. The main forms of precipitation include drizzle, rain, sleet, snow, ice pellets, graupel and hail. ...

. As precipitation, primarily

rain Rain is water droplets that have condensed from atmospheric water vapor and then fall under gravity. Rain is a major component of the water cycle and is responsible for depositing most of the fresh water on the Earth. It provides water f ...

, falls in the downdraft, it evaporates in the unsaturated air, leading to cooling in the downdraft due to an absorption of

latent heat Latent heat (also known as latent energy or heat of transformation) is energy released or absorbed, by a body or a thermodynamic system, during a constant-temperature process — usually a first-order phase transition. Latent heat can be understo ...

. The cooling of the air leads to an increase in the pressure as the air becomes denser. While not the primary mechanism behind the mesohigh, melting or sensible cooling of

hail Hail is a form of solid precipitation. It is distinct from ice pellets (American English "sleet"), though the two are often confused. It consists of balls or irregular lumps of ice, each of which is called a hailstone. Ice pellets generally fal ...

can also lead to increased pressure in the mesohigh. An additional source of increased pressure is hydrometeor loading, the weight of precipitation increasing the speed of the downdraft, leading to increased pressure as the air converges at the surface. While hydrometeor loading is not a main contributor of increased pressure to the mesohigh, and it is a non-hydrostatic process, it can increase the pressure as much as 2 mb.

References

{{Climate-stub Mesoscale meteorology fr:Anticyclone#Anticyclone de méso-échelle

Formation

See also

References