Brunt-Vaisala Frequency
D1. Physical and chemical oceanography and marine meteorologyDefinition
Natural frequency of vertical oscillation in a stratified fluid.
The Brunt-Vaisala (buoyancy) frequency N is the natural frequency at which a displaced parcel oscillates vertically in a stably stratified fluid; N^2 is proportional to the vertical gradient of potential density. A large N marks strong stratification (the pycnocline) that suppresses vertical motion and sets the upper frequency limit for internal waves. It enters the Richardson number, internal-wave dispersion, and the scaling of ocean turbulence.