Spectral analysis of tropical atmospheric dynamical variables using a linear shallow water modal decomposition

Space-time spectral analysis has been used frequently in studying observational evidence of convectively coupled equatorial waves. Here 20 years of brightness temperature and dynamical reanalysis data are analyzed by an appropriate projection onto the meridional basis functions of the β-plane linear shallow water equations. Evidence of peaks in power along linear equatorial mode dispersion curves in brightness temperature, zonal and meridional wind, divergence and geopotential spectra are presented.

The main feature of all space-time spectra considered is the redness in frequency, zonal wave number and meridional mode number. It is found that spectral peaks in the dynamical variables spectra are largely consistent with linear shallow water theory, with spectral peaks related to barotropic waves and extratropical storm track activity appearing as well. The convectively coupled wave signals are seen to be confined to the first few meridional basis functions suggesting a potential for reducing noise when filtering for these signals and possible implications for future modeling work.