EGU21-724, updated on 03 Mar 2021
EGU General Assembly 2021
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

The Art of Identifying Equatorial Waves

Peter Knippertz1, Juliana Dias2, Andreas H. Fink1, Maria Gehne2, George Kiladis2, Kazuyoshi Kikuchi3, John Methven4, Athul Rasheeda Satheesh1, Paul E. Roundy5, Andreas Schlueter6, Matthew C. Wheeler7, Steven J. Woolnough4, Gui-Ying Yang4, and Nedjeljka Žagar8
Peter Knippertz et al.
  • 1Institute of Meteorology and Climate Research, Karlsruhe Institute of Technology, Karlsruhe, Germany (
  • 2NOAA Physical Sciences Laboratory, Boulder, CO, USA
  • 3School of Ocean and Earth Science and Technology, University of Hawaii at Manoa, Honolulu, HI, USA
  • 4Department of Meteorology, University of Reading, Reading, UK
  • 5Department of Atmospheric and Environmental Sciences, University at Albany, NY, USA
  • 6Department of Computer Science, Stanford University, Stanford, CA, USA
  • 7Bureau of Meteorology, Melbourne, Australia
  • 8Meteorological Institute, University of Hamburg, Hamburg, Germany

Equatorial waves are synoptic- to planetary-scale propagating disturbances at low latitudes with frequencies from a few days to several weeks. Here this term includes Kelvin waves, equatorial Rossby waves, mixed-Rossby gravity waves, and inertio-gravity waves, which are closely related to linear wave theory, but also tropical disturbances, African easterly waves, and the intraseasonal Madden-Julian Oscillation. These waves can couple with deep convection, leading to a substantial modulation of rainfall. Recent work has shown that equatorial waves are amongst the dynamical features internal to the troposphere with the longest intrinsic predictability and that some models forecast them with an exploitable level of skill at lead times of up to a few weeks.

A number of methods have been developed to identify and objectively isolate equatorial waves, both in (usually satellite) observations and in model fields. Most of these rely on (or at least refer to) the adiabatic, frictionless linearized primitive equations or shallow water system on the tropical beta plane. Common ingredients to these methods are longitude-time filtering (Fourier or wavelet) and/or projections onto predefined empirical or theoretical dynamical patterns. This paper aims to give an overview of the different methods to isolate the waves and their structures, to discuss underlying assumptions, to provide a systematic comparison, and to reveal advantages and disadvantages of each method. This way this study helps to optimally choose an approach suited to a given problem at hand and to avoid misuse and misinterpretation of the results.

How to cite: Knippertz, P., Dias, J., Fink, A. H., Gehne, M., Kiladis, G., Kikuchi, K., Methven, J., Rasheeda Satheesh, A., Roundy, P. E., Schlueter, A., Wheeler, M. C., Woolnough, S. J., Yang, G.-Y., and Žagar, N.: The Art of Identifying Equatorial Waves, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-724,, 2021.

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