# Buoyancy frequency

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**Buoyancy frequency** is the frequency with which a parcel or particle of fluid displaced a small vertical distance from its equilibrium position in a stable environment will oscillate. This concept, also termed the **Brunt–Väisälä frequency**, can apply to a liquid or gaseous medium. The parcel will oscillate in simple harmonic motion with an angular frequency defined by:

where **g** is the gravitational acceleration, **θ** is the potential temperature, **α** is the thermal expansion coefficient, and **β** is the saline contraction coefficient. In practice, the equivalent formula:

is often used, where **c** is the velocity of sound, although care must be taken to consistently evaluate **ρ** and **c**.

**Further Reading:**

- Physical Oceanography Index
- J. S. Turner. Buoyancy Effects in Fluids. Cambridge Univ. Press, 1973.
- Trevor McDougall, Steve Thorpe, and Carl Gibson. Small-scale turbulence and mixing in the ocean: a glossary. In J. Nihoul and B. Jamart, editors, Small-Scale Turbulence and Mixing in the Ocean, pages 3-9. Elsevier, 1987.

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