Identification of equatorial waves using Hough function vectors

Abstract

Equatorial waves are essential features of the tropical atmosphere dynamics, and their diagnosis is relevant for both operational and climate analysis. Here, we present a method for the identification of equatorial waves using the multivariate spatial structures of the eigensolutions of the linearized shallow-water equations over the sphere, named Hough function vectors. The method does not require any a priori space–time filtering to separate westward- and eastward-moving waves, and it can be applied to instantaneous or daily circulation fields. The wave types (Kelvin, Rossby, mixed Rossby–gravity, inertio-gravity) are unambiguously identified by the intrinsic dynamical relationship between the horizontal wind components and geopotential fields represented in the multivariate meridional structures of the Hough function vectors. Both free and convectively coupled equatorial waves can be diagnosed. Moreover, different time filterings can be applied a posteriori, depending on the purposes of the analysis. This article is written as a proof of concept, and direct comparisons are made with results of other methods recently reviewed in a work published in this journal.