02 Sep 2022
02 Sep 2022
Status: this preprint is currently under review for the journal WCD.

Identifying quasi-periodic variability using multivariate empirical mode decomposition: a case of the tropical Pacific

Lina Boljka, Nour-Eddine Omrani, and Noel S. Keenlyside Lina Boljka et al.
  • Geophysical Institute, University of Bergen and Bjerknes Centre for Climate Research, Bergen, Norway

Abstract. Tropical Pacific is home to climate variability on different timescales, including El Niño Southern Oscillation (ENSO) – one of the most prominent quasi-periodic modes of variability in the Earth’s climate system. It is a coupled atmosphere-ocean mode of variability with a 2-8-year-timescale and oscillates between a warm (El Niño) and a cold (La Niña) phase. However, the dynamics of ENSO is complex, involving a variety of spatial and temporal scales as well as their interactions, which are not necessarily well understood. We use a recently developed nonlinear and nonstationary multivariate timeseries analysis tool – multivariate empirical mode decomposition (MEMD) – to revisit quasi-periodic variability within ENSO. MEMD is a powerful tool for objectively identifying (intrinsic) timescales of variability within a given system. We apply it to reanalysis and observational data as well as to climate model output (NorCPM1). Observational/reanalysis data reveal a quasi-periodic variability in the tropical Pacific on timescales ~2–4.5 years. This variability can then be related to ENSO’s recharge-discharge and simplified West-Pacific oscillator conceptual models. The latter occurs only on this timescale and is not necessarily well represented in NorCPM1. Additionally, the ~2–4.5-year variability in ENSO can be 'predicted' up to ~20 months ahead, while predicting the full ENSO amplitude remains challenging. MEMD can therefore be used for assessing climate dynamics on different timescales and for evaluating their representation in climate models.

Lina Boljka et al.

Status: open (until 14 Oct 2022)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • CC1: 'Non-linearity comment', Paul PUKITE, 05 Sep 2022 reply
    • AC1: 'Reply on CC1', Lina Boljka, 15 Sep 2022 reply
  • RC1: 'Comment on wcd-2022-51', Anonymous Referee #1, 30 Sep 2022 reply

Lina Boljka et al.

Lina Boljka et al.


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Short summary
This study examines quasi-periodic variability in the tropical Pacific on interannual timescales and related physics using a recently developed timeseries analysis tool. We find that wind stress in the West-Pacific and recharge-discharge of ocean heat content are likely related to each other on ~2–4.5-year timescales (but not on other) and dominate variability in sea surface temperatures on those timescales. Further implications for climate models and long-term prediction are also discussed.