Brunt-Väisälä frequency

In the dynamics of atmospheric processes and in oceanography, the Brunt-Väisälä frequency , or buoyancy frequency , is the frequency with which a vertically deflected mass element oscillates in a static system. She is in the atmosphere

${\displaystyle N\equiv {\sqrt {{\frac {g}{\theta }}{\frac {d\theta }{dz}}}}}$ .

Mean:

• ${\displaystyle \theta }$the potential temperature , d. H. the temperature that the system would assume if it were transferred to a specified standard pressure level (1000 hPa) due to an adiabatic change in state ,
• ${\displaystyle g}$the acceleration due to gravity and
• ${\displaystyle z}$ the height.

In water, where the density does not vary in direct proportion to the temperature, the following applies

${\displaystyle N\equiv {\sqrt {-{\frac {g}{\rho }}{\frac {d\rho }{dz}}}}}$ .

Here is

• ${\displaystyle \rho }$the potential density .

The Brunt-Väisälä frequency was named after David Brunt (1886-1965) and Vilho Väisälä .

context

The Brunt-Väisälä frequency characterizes dynamic processes in a statically stable stratified medium (air, water).

In a statically unstable medium, vertically deflected mass elements do not oscillate, but continue to move in the direction of the original deflection.