A revised method of presenting wavenumber–frequency power spectrum diagrams that reveals the asymmetric nature of tropical large-scale waves

Abstract

The popular method of presenting wavenumber-frequency power spectrum diagrams for studying tropical large-scale in the literature is shown to give an incomplete presentation of these waves. The so-called convectively-coupled Kelvin (mixed Rossby-gravity) waves are presented as existing only in the symmetric (antisymmetric) component of the diagrams. This is obviously not consistent with the published composite/regression studies of convectively-coupled Kelvin waves, which illustrate the asymmetric nature of these waves. The cause of this inconsistency is revealed in this note and a revised method of presenting the power spectrum diagrams is proposed. When this revised method is used, convectively-coupled Kelvin waves do show anti-symmetric components, and convectively-coupled mixed Rossby-gravity (also known as Yanai waves) do show a hint of symmetric components. These results bolster a published proposal that these be called chimeric Kelvin waves, chimeric mixed Rossby-gravity waves, etc. This revised method of presenting power spectrum diagrams offers a more rigorous means of comparing the General Circulation Models (GCM) output with observations by calling attention to the capability of GCMs in correctly simulating the asymmetric characteristics of the equatorial waves.