Convectively coupled equatorial-wave diagnosis using three-dimensional normal modes

Abstract

A new methodology for the diagnosis of convectively coupled equatorial waves (CCEWs) is presented. It is based on a pre-filtering of the geopotential and horizontal wind, using three-dimensional (3D) normal mode functions of the adiabatic linearized equations of a resting atmosphere, followed by a space–time spectral analysis to identify the spectral regions of coherence. Themethodology permits a direct detection of various types of equatorialwave, compares the dispersion characteristics of the coupled waves with the theoretical dispersion curves and allows an identification of which vertical modes are more involved in the convection. Moreover, the proposed methodology is able to show the existence of free dry waves and moist coupled waves with a common vertical structure, which is in conformity with the effect of convective heating/cooling on the effective static stability, as deduced from the gross moist stability concept. The methodology is also sensitive to wave interactions. Themethodology has been applied to the ERA-Interim horizontal wind and geopotential height fields and to the interpolated outgoing long-wave radiation (OLR) data produced by the National Oceanic and Atmospheric Administration. The results obtained provide examples of the aforementioned effects.