Baroclinic Instability

Baroclinic Instability is a fluid dynamic instability which helps to understand some important features of the so-called large scale waves in the mid-latitude atmosphere. These waves provide a mechanism for transporting heat and angular momentum and are believed to control the temperature gradient between the equator and the pole. The first

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accurate theoretical model to include baroclinic instability was the one developed by Jule Charney in 1947. He considered

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a simplified version of the equations of motion for the atmosphere in which the scaling is made for small Rossby number

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and a stratified fluid. The approximate equations are known as quasi-geostrophic system. In the Charney formulation the

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effect of the rotation of the earth is approximated by the so-called beta plane. A simplified version of the baroclinic

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instability was proposed independently by Eady in 1949. Eady considered constant vertical shear, no beta and a upper lid.

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The balance between Coriolis forces due to rotation and buoyancy forces can create a fluid which is unstable. Potential energy can be trapped in sloping density surfaces, and released in the form of fluid motions known as baroclinic waves.

Related Topics:
Coriolis force - Baroclinic waves

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Baroclinic instability can be investigated in the laboratory using a rotating, fluid filled annulus. This is heated at the outer wall (think equator) and cooled at the inner wall (think pole) and the resulting fluid flows give rise to baroclinic waves.

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This experimental system gives rise to a rich range of complex non-linear dynamics and has been the source of a large body of academic research over the last 50 years.

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