Preprints
https://doi.org/10.5194/wcd-2021-21
https://doi.org/10.5194/wcd-2021-21

  30 Apr 2021

30 Apr 2021

Review status: this preprint was under review for the journal WCD but the revision was not accepted.

Observed wavenumber-frequency spectrum of global, normal mode function decomposed, fields: a possible evidence for nonlinear effects on the wave dynamics

André Seiji Wakate Teruya1, Breno Raphaldini2, Victor Chavez Mayta3, Carlos Frederico Mendonça Raupp1, and Pedro Leite da Silva Dias1 André Seiji Wakate Teruya et al.
  • 1Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo, Sao Paulo, Brazil
  • 2Department of Mathematical Sciences, Durham University, Durham, UK
  • 3Department of Climate and Space Science and Engineering, University of Michigan, Ann Arbor, Michigan, and Department of Atmospheric and Oceanic Sciences, University of Wisconsin-Madison, Madison, United States

Abstract. The study of tropical tropospheric disturbances has led to important challenges from both observational and theoretical points of view. In particular, the observed wavenumber-frequency spectrum of tropical oscillations, also known as Wheeler-Kiladis diagram, has helped bridging the gap between observations and the linear theory of equatorial waves. Here we have obtained a similar wavenumber-frequency spectrum for each equatorial wave type by performing a normal mode function (NMF) decomposition of global Era-Interim reanalysis data, with the NMF basis being given by the eigensolutions of the primitive equations in spherical coordinates, linearized around a resting background state. In this methodology, the global multi-level horizontal velocity and geopotential height fields are projected onto the normal mode functions characterized by a vertical mode, a zonal wavenumber, a meridional quantum index and a mode type, namely Rossby, Kelvin, mixed Rossby-gravity and westward and eastward propagating inertio-gravity modes. The horizontal velocity and geopotential height fields associated with each mode type are then reconstructed on the physical space, and the corresponding wavenumber-frequency spectrum is calculated for the 200 hPa zonal wind. The results reveal some expected structures, such as the dominant global-scale Rossby and Kelvin waves constituting the intraseasonal frequency associated with the Madden-Julian Oscillation. On the other hand, some unexpected features such as westward propagating Kelvin waves and eastward propagating westward inertio-gravity waves are also revealed by our observed 200 hPa zonal wind spectrum. These intriguing behaviours represent a large departure from the linear equatorial wave theory and can be a result of strong nonlinearities in the wave dynamics.

André Seiji Wakate Teruya et al.

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on wcd-2021-21', Anonymous Referee #1, 23 May 2021
    • AC1: 'Reply on RC1', Andre Teruya, 04 Jun 2021
  • RC2: 'Comment on wcd-2021-21', Anonymous Referee #2, 26 May 2021
  • RC3: 'Comment on wcd-2021-21', Anonymous Referee #3, 05 Jun 2021

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on wcd-2021-21', Anonymous Referee #1, 23 May 2021
    • AC1: 'Reply on RC1', Andre Teruya, 04 Jun 2021
  • RC2: 'Comment on wcd-2021-21', Anonymous Referee #2, 26 May 2021
  • RC3: 'Comment on wcd-2021-21', Anonymous Referee #3, 05 Jun 2021

André Seiji Wakate Teruya et al.

André Seiji Wakate Teruya et al.

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Short summary
The dynamics of the equatorial troposphere is incredibly complex. Several types of waves constitute the core of the theoretical understanding of tropical dynamics. Signatures of these waves are observed in the spectrum of atmospheric variables. We decompose the atmospheric winds into their wave contributions. A spectral analysis of these fields reveal important departures from the linear theory of equatorial waves, suggesting a possible role of nonlinearity in the propagation of these waves.