Identifying convectively coupled equatorial waves using theoretical wave eigenvectors

Convectively coupled equatorial waves (CCEWs) are often identified by space-time filtering techniques which make use of the eigenvalues of linear shallow water theory. Here, instead, a method is presented for identifying CCEWs by projection onto the eigenvectors of the theory. This method does not use space-time filtering; instead, wave signals corresponding to the first baroclinic Kelvin, Rossby, and mixed Rossby-gravity (MRG) waves are constructed from reanalysis data by a series of projections onto (i) vertical and meridional modes and (ii) the wave eigenvectors. In accordance with the theory, only dry variables, i.e. winds and geopotential height, are used; no proxy for convection is used. Using lag-lead regression, composites of the structures associated with each eigenvector signal during boreal summer are shown to contain all the features of the theory as well as some additional features seen in previous observational studies, such as vertical tilts. In addition, these composites exhibit propagation in good agreement with the theory; for the Kelvin and MRG composites, this agreement is strongest over the Pacific ITCZ, while the Rossby composite exhibits strongest agreement over the Pacific warm pool. The eigenvector signals are also in good agreement with space-time filtered outgoing longwave radiation (OLR) for the Kelvin wave, and reasonable agreement for the Rossby and MRG waves, and it is shown that the eigenvector projections used here contribute to this agreement. Finally, a space-time filtered version of the eigenvector projection is briefly discussed, as are potential applications of the method.