The turbopause, also known as the homopause, marks the altitude in an atmosphere below which

turbulent mixing In fluid dynamics, turbulence or turbulent flow is fluid motion characterized by chaotic changes in pressure and flow velocity. It is in contrast to a laminar flow, which occurs when a fluid flows in parallel layers, with no disruption between ...

dominates. Mathematically, it is defined as the point where the coefficient of

Eddy diffusion Eddy diffusion, eddy dispersion, or turbulent diffusion is a process by which substances are mixed in the atmosphere, the ocean or in any fluid system due to eddy motion. In other words, it is mixing that is caused by eddies that can vary in size f ...

is equal to the coefficient of

molecular diffusion Molecular diffusion, often simply called diffusion, is the thermal motion of all (liquid or gas) particles at temperatures above absolute zero. The rate of this movement is a function of temperature, viscosity of the fluid and the size (mass) of ...

. The region below the turbopause is known as the

homosphere The homosphere is the layer of an atmosphere where the bulk gases are homogeneously mixed due to turbulent mixing or eddy diffusion. The bulk composition of the air is mostly uniform so the concentrations of molecules are the same throughout the h ...

, where the atmosphere is well mixed for chemical species which have long

mean residence time The residence time of a fluid parcel is the total time that the parcel has spent inside a control volume (e.g.: a chemical reactor, a Lake retention time, lake, a human body). The residence time of a Set (mathematics), set of parcels is quantified ...

s. 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 The heterosphere is the layer of an atmosphere where the gases are separated out by molecular diffusion with increasing altitude such that lighter species become more abundant relative to heavier species. The heavier molecules and atoms tend to be p ...

, where

dominates and the chemical composition of the atmosphere varies according to chemical species and their atomic weight. The Earth's turbopause lies near the

mesopause The mesopause is the point of minimum temperature at the boundary between the mesosphere and the thermosphere atmospheric regions. Due to the lack of solar heating and very strong radiative cooling from carbon dioxide, the mesosphere is the cold ...

, at the intersection of the mesosphere 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 90 km (56 mi). Some other turbopauses in the solar system that are known include Venus' turbopause at about 130 – 135 km, Mars' at about 130 km, Jupiter's at roughly 385 km, and Titan's at around 800 – 850 km. It was discovered by French scientists following the firing of two Véronique sounding rockets March 10th and 12th, 1959.

References

* ;Specific {{Portal bar, Earth sciences, Weather, Environment, Astronomy, Stars, Science Atmospheric boundaries Atmosphere of Earth