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The Generation of African Waves

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  • 1 University of Illinois, Urbana-Champaign
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Abstract

A linearized, pseudo-spectral, primitive equation model is used to simulate the response of the low-level easterly jet over northern Africa to perturbations on the scale of African waves. The model results show that the jet is unstable due to both its horizontal and vertical shears. The most unstable wave supported by the jet has a wavelength of 3O00 km and a period of 2.0–2.5 days. It attains its maximum intensity at the 700 mb level, near 14°N. This compares favorably with the characteristics of the observed waves.

The kinetic energy of the waves grows at the expense of the kinetic energy of the mean jet. Energy is transferred at approximately equal rates by the horizontal and vertical Reynolds stresses. Energy conversions involving available potential energy are nearly an order of magnitude smaller, reflecting the fact that the kinetic energy of the wave accounts for about 90% of the total wave energy.

The characteristics of the most unstable wave are virtually unchanged when a crude parameterization of latent heat release is included in the model.

Abstract

A linearized, pseudo-spectral, primitive equation model is used to simulate the response of the low-level easterly jet over northern Africa to perturbations on the scale of African waves. The model results show that the jet is unstable due to both its horizontal and vertical shears. The most unstable wave supported by the jet has a wavelength of 3O00 km and a period of 2.0–2.5 days. It attains its maximum intensity at the 700 mb level, near 14°N. This compares favorably with the characteristics of the observed waves.

The kinetic energy of the waves grows at the expense of the kinetic energy of the mean jet. Energy is transferred at approximately equal rates by the horizontal and vertical Reynolds stresses. Energy conversions involving available potential energy are nearly an order of magnitude smaller, reflecting the fact that the kinetic energy of the wave accounts for about 90% of the total wave energy.

The characteristics of the most unstable wave are virtually unchanged when a crude parameterization of latent heat release is included in the model.

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