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In atmospheric dynamics, oceanography, and geophysics, the Brunt-Väisälä frequency, or buoyancy frequency, is the frequency at which a vertically displaced parcel will oscillate within a statically stable environment. In the atmosphere,## Context

The concept derives from Newton's Second Law when applied to a fluid parcel in the presence of a background
stratification (in which the density changes in the vertical). The parcel, perturbed vertically from its
starting position, experiences a vertical acceleration. If the acceleration is back towards the initial
position, the stratification is said to be stable and the parcel oscillates vertically. In this case, N^{2}>0 and the frequency of oscillation is given by N. If the acceleration is away from
the initial position (N^{2}<0), the stratification is unstable. In this case, overturning
or convection generally ensues.

- $N\; equiv\; sqrt\{frac\{g\}\{theta\}frac\{dtheta\}\{dz\}\}$, where $theta$ is potential temperature, $g$ is the local acceleration of gravity, and $z$ is geometric height.

In the ocean where salinity is important, or in fresh water lakes near freezing, where density is not a linear function of temperature,

- $N\; equiv\; sqrt\{-frac\{g\}\{rho\}frac\{drho\}\{dz\}\}$, where $rho$, the potential density, depends on both temperature and salinity.

The Brunt-Väisälä frequency relates to internal gravity waves and provides a useful description of atmospheric and oceanic stability.

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Last updated on Wednesday September 03, 2008 at 21:52:38 PDT (GMT -0700)

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This article is licensed under the GNU Free Documentation License.

Last updated on Wednesday September 03, 2008 at 21:52:38 PDT (GMT -0700)

View this article at Wikipedia.org - Edit this article at Wikipedia.org - Donate to the Wikimedia Foundation

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