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Earth and Space Sciences · Glossary

What is Zonal mean and eddies?

Also known as: zonal mean · eddy (atmospheric)

Definition 20.11 University Earth and Space Sciences — Year 3 · Chapter 20 — Atmospheric Dynamics

The zonal mean of a quantity AA is its average round a latitude circle at fixed height or pressure, [A]=(1/2π)∫02πA dλ[A] = (1/2\pi)\int_0^{2\pi} A\,\mathrm d\lambda. The departure A∗=A−[A]A^* = A - [A] is its eddy part; an eddy of the atmosphere is any departure of the flow from its zonal mean: travelling waves, stationary waves, cyclones and anticyclones.

A growing baroclinic wave in plan view (schematic, Northern Hemisphere, westerly flow). The isotherm (dashed) lags the streamline by a quarter wavelength or less, so the air moving north (red arrows) is warmer than the air moving south at the same latitude (blue): the wave carries heat poleward, [v*T*] > 0.
A growing baroclinic wave in plan view (schematic, Northern Hemisphere, westerly flow). The isotherm (dashed) lags the streamline by a quarter wavelength or less, so the air moving north (red arrows) is warmer than the air moving south at the same latitude (blue): the wave carries heat poleward, [v∗T∗]>0[v^*T^*] > 0.
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