The turbopause, also called the homopause, marks the altitude in an atmosphere below which
turbulent mixing dominates. Mathematically, it is defined as the point where the coefficient of
Eddy diffusion is equal to the coefficient of
molecular diffusion
Molecular diffusion is the motion of atoms, molecules, or other particles of a gas or liquid at temperatures above absolute zero. The rate of this movement is a function of temperature, viscosity of the fluid, size and density (or their product, ...
. The region below the turbopause is known as the
homosphere, where the atmosphere is well mixed for chemical species which have long
mean residence times. Highly reactive chemicals tend to have variable concentration throughout the atmosphere, while unreactive species have more homogeneous concentrations. The region above the turbopause is the
heterosphere, where
molecular diffusion
Molecular diffusion is the motion of atoms, molecules, or other particles of a gas or liquid at temperatures above absolute zero. The rate of this movement is a function of temperature, viscosity of the fluid, size and density (or their product, ...
dominates and the chemical composition of the atmosphere varies according to chemical species and their atomic weight.
Earth's turbopause lies near the
mesopause, at the intersection of the
mesosphere
The mesosphere (; ) is the third layer of the atmosphere, directly above the stratosphere and directly below the thermosphere. In the mesosphere, temperature decreases as altitude increases. This characteristic is used to define limits: it be ...
and the
thermosphere
The thermosphere is the layer in the Earth's atmosphere directly above the mesosphere and below the exosphere. Within this layer of the atmosphere, ultraviolet radiation causes photoionization/photodissociation of molecules, creating ions; the ...
, at an altitude of roughly . Some other turbopauses in the
Solar System
The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Sola ...
that are known include
Venus' turbopause at about ,
Mars' at about ,
Jupiter's at roughly , and
Titan's at around .
It was discovered by
French scientists following the firing of two
Véronique sounding rockets on 10 and 12 March 1959.
References
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Atmospheric boundaries
Atmosphere of Earth
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