Barotropy

Under barotropy (from Greek baros "pressure" and tropos "rotation direction") is defined as the property of the density of a fluid only from the pressure to depend . This leads to areas of the same pressure ( isobars ) and the same temperature ( isotherms ) running parallel to one another. The counterpart to barotropy is baroclinity . ${\displaystyle \rho }$ ${\displaystyle p}$ ${\displaystyle \rho =\rho {}(p)}$

The images show extremely exaggerated tendencies, which in reality are usually extremely small and therefore difficult to measure.

Barotropy in the atmosphere

Barotropic atmosphere

In the barotropic atmosphere the surfaces of the same temperature are parallel to those of the same pressure. Therefore the mean temperature between two surfaces of the same pressure is the same everywhere and its slope is constant with the altitude. This results in a constant wind speed in terms of amount and direction .

Barotropy in the ocean

Barotropic ocean

In the ocean , barotropic conditions are assumed, especially in the depths assumed to be relatively homogeneous .

The isopycne surfaces (surfaces of constant density) and the isobar surfaces are directed parallel to each other. Their inclination remains constant with increasing depth. Therefore, the horizontal pressure gradient from B to A and the geostrophic flow are constant with depth.

Barotropic phenomenon

The barotropic phenomenon (also barotropic inversion) occurs in mixtures of two substances with different molecular weights in certain temperature, mixture and pressure ranges, if the coexistence of liquid and gaseous phases, the gas phase has the greater density and sinks below the liquid. The phenomenon was discovered in 1906. Heike Kamerlingh Onnes discovered with Keesom that when gaseous helium was compressed over liquid hydrogen, the gas was stored below the liquid at pressures above 30 bar and temperatures of around 20 degrees Kelvin.

astrophysics

In astrophysics, for example, polytropic equations of state of form are often used in theoretical investigations of the star structure

${\displaystyle p=K\cdot \rho ^{\gamma }}$

with the pressure p, the density , the polytropic constant K and the polytropic index , which was used by Robert Emden for simple star models. For ideal non-relativistic gases , for relativistic gases (like the degenerate electron gas in white dwarfs) . In this case, polytropy is a special case of barotropy. ${\displaystyle \rho }$ ${\displaystyle \gamma =1+{\frac {1}{n}}}$ ${\displaystyle n={\frac {3}{2}}}$ ${\displaystyle n=3}$

Barotropy in soil mechanics

In soil mechanics , barotropy denotes the dependence of the angle of friction on the mean pressure level. The angle of friction decreases with increasing mean pressure.

The phenomenon is usually neglected and is mostly only used when considering low stress states.

literature

• Walter Roedel: Physics of our environment: the atmosphere. Springer Verlag, Berlin 2000, ISBN 3-540-67180-3 .
• Gösta H. Liljequist, Konrad Cehak: General Meteorology. Springer-Verlag, Berlin 1984, ISBN 3-540-41565-3 .
• Dimitrios Kolymbas: Geotechnics - soil mechanics and foundation engineering. Springer Verlag, Berlin 1998, ISBN 3-540-62806-1 .

Individual evidence

1. ^ Spectrum Lexicon of Physics, 1998, Volume 1, p. 239
2. ^ JS Rowlinson, James Dewar, Ashgate 2012, p. 139
3. ↑ For example Polytrop , Spectrum Lexicon Astronomie
4. ↑ Cf. Dimitrios Kolymbas: Geotechnics - Soil Mechanics and Foundation. Springer Verlag, Berlin 1998, p. 104.