Convective overshoot
Encyclopedia
Convective overshoot is a phenomenon of convection
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....

 carrying material beyond an unstable region of the atmosphere
Atmosphere
An atmosphere is a layer of gases that may surround a material body of sufficient mass, and that is held in place by the gravity of the body. An atmosphere may be retained for a longer duration, if the gravity is high and the atmosphere's temperature is low...

 into a stratified, stable region. Overshoot is caused by the momentum
Momentum
In classical mechanics, linear momentum or translational momentum is the product of the mass and velocity of an object...

 of the convecting material, which carries the material beyond the unstable region.

Deep, moist convection in Earth's atmosphere

Main article: Overshooting top
Overshooting top
An overshooting top is a dome-like protrusion that shoots out of the top of the anvil of a thunderstorm. When an overshooting top is present for 10 minutes or longer, it is a strong indication that the thunderstorm may be severe....


One example is thermal
Thermal
A thermal column is a column of rising air in the lower altitudes of the Earth's atmosphere. Thermals are created by the uneven heating of the Earth's surface from solar radiation, and are an example of convection. The sun warms the ground, which in turn warms the air directly above it...

 columns extending above the top of the equilibrium level
Equilibrium level
In meteorology, the equilibrium level , or level of neutral buoyancy , or limit of convection , is the height at which a rising parcel of air is at a temperature of equal warmth to it....

 (EL) in thunderstorm
Thunderstorm
A thunderstorm, also known as an electrical storm, a lightning storm, thundershower or simply a storm is a form of weather characterized by the presence of lightning and its acoustic effect on the Earth's atmosphere known as thunder. The meteorologically assigned cloud type associated with the...

s: unstable air rising from (or near) the surface normally stops rising at the EL (near the tropopause
Tropopause
The tropopause is the atmospheric boundary between the troposphere and the stratosphere.-Definition:Going upward from the surface, it is the point where air ceases to cool with height, and becomes almost completely dry...

) and spreads out as an anvil cloud; but in the event of a strong updraft, unstable air is carried past the EL as an overshooting top
Overshooting top
An overshooting top is a dome-like protrusion that shoots out of the top of the anvil of a thunderstorm. When an overshooting top is present for 10 minutes or longer, it is a strong indication that the thunderstorm may be severe....

or dome. A parcel
Air parcel
In fluid dynamics, within the framework of continuum mechanics, a fluid parcel is a very small amount of fluid, identifiable throughout its dynamic history while moving with the fluid flow. As it moves, the mass of a fluid parcel remains constant, while—in a compressible flow—its volume may...

 of air will stop ascending at the maximum parcel level
Maximum parcel level
The maximum parcel level is the highest level in the atmosphere that a moist convectively rising air parcel will reach after ascending through the free convective layer and reaching the equilibrium level , near the tropopause...

 (MPL). This overshoot is responsible for most of the turbulence
Turbulence
In fluid dynamics, turbulence or turbulent flow is a flow regime characterized by chaotic and stochastic property changes. This includes low momentum diffusion, high momentum convection, and rapid variation of pressure and velocity in space and time...

 experienced in the cruise phase of commercial air flights.

Stellar convection

Another example of convective overshoot is at the base of the convection zone
Convection zone
The convection zone of a star is the range of radii in which energy is transported primarily by convection. In the radiation zone, energy is transported by radiation...

 in the solar interior
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...

. The heat of the Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...

's thermonuclear fusion is carried outward by radiation
Radiation
In physics, radiation is a process in which energetic particles or energetic waves travel through a medium or space. There are two distinct types of radiation; ionizing and non-ionizing...

 in the deep interior radiation zone
Radiation zone
The radiation zone is the middle zone in the Sun's interior. Energy travels out of the core into the radiation zone. Energy that travels through the radiation zone is in the form of electromagnetic radiation. The radiation zone is so dense that the waves bounce around...

 and by convective circulation in the outer convection zone
Convection zone
The convection zone of a star is the range of radii in which energy is transported primarily by convection. In the radiation zone, energy is transported by radiation...

, but cool sinking material from the surface penetrates farther into the radiative zone than theory would suggest. This affects the heat transfer rate and the temperature of the solar interior which can be indirectly measured by helioseismology
Helioseismology
Helioseismology is the study of the propagation of wave oscillations, particularly acoustic pressure waves, in the Sun. Unlike seismic waves on Earth, solar waves have practically no shear component . Solar pressure waves are believed to be generated by the turbulence in the convection zone near...

. The layer between the Sun's convective and radiative zone is called the tachocline
Tachocline
The tachocline is the transition region of the Sun between the radiative interior and the differentially rotating outer convective zone. It is in the outer third of the sun . This causes the region to have a very large shear as the rotation rate changes very rapidly...

.
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