Preprints
https://doi.org/10.5194/egusphere-2023-1861
https://doi.org/10.5194/egusphere-2023-1861
04 Oct 2023
 | 04 Oct 2023

Changing effects of external forcing on Atlantic-Pacific interactions

Soufiane Karmouche, Evgenia Galytska, Gerald A. Meehl, Jakob Runge, Katja Weigel, and Veronika Eyring

Abstract. Recent studies have highlighted the increasingly dominant role of external forcing in driving Atlantic and Pacific Ocean variability during the second half of the 20th century. This paper provides insights into the underlying mechanisms driving interactions between modes of variability over the two basins. We define a set of possible drivers of these interactions and apply causal discovery to reanalysis data, an ensemble of pacemaker simulations where the observed El Niño Southern Oscillation (ENSO) is prescribed, and a pre-industrial control simulation. We also utilize large ensemble means of historical simulations from the Coupled Model Intercomparison Project Phase 6 (CMIP6) to quantify the effect of external forcing and improve the understanding of its impact. By conducting a causal analysis of the historical time series, a regime switch is identified in the interactions between major modes of Atlantic and Pacific climate variability. Causal networks derived from pacemaker simulations support this finding and further demonstrate that the effect of external forcing could favor an Atlantic-driven regime between 1985 and 2014 where warming tropical North Atlantic sea surface temperatures induce a La Niña-like cooling in the equatorial Pacific during the following season through a strengthening of the Pacific Walker Circulation. This negative sign effect was not detected when the historical external forcing signal is removed in the pacemaker ensemble. The analysis of the pre-industrial control run further supports the notion that the Atlantic and Pacific modes of natural climate variability exert contrasting impacts on each other even in the absence of external forcing. We show that causal discovery can quantify previously unknown connections and thus provides important potential to contribute to a deeper understanding of the mechanisms driving changes in regional and global climate variability.

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Journal article(s) based on this preprint

11 Jun 2024
Changing effects of external forcing on Atlantic–Pacific interactions
Soufiane Karmouche, Evgenia Galytska, Gerald A. Meehl, Jakob Runge, Katja Weigel, and Veronika Eyring
Earth Syst. Dynam., 15, 689–715, https://doi.org/10.5194/esd-15-689-2024,https://doi.org/10.5194/esd-15-689-2024, 2024
Short summary
Soufiane Karmouche, Evgenia Galytska, Gerald A. Meehl, Jakob Runge, Katja Weigel, and Veronika Eyring

Interactive discussion

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2023-1861', Anonymous Referee #1, 26 Oct 2023
    • AC1: 'Reply on RC1', Soufiane Karmouche, 07 Feb 2024
  • RC2: 'Comment on egusphere-2023-1861', Anonymous Referee #2, 15 Nov 2023
    • AC2: 'Reply on RC2', Soufiane Karmouche, 07 Feb 2024

Interactive discussion

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2023-1861', Anonymous Referee #1, 26 Oct 2023
    • AC1: 'Reply on RC1', Soufiane Karmouche, 07 Feb 2024
  • RC2: 'Comment on egusphere-2023-1861', Anonymous Referee #2, 15 Nov 2023
    • AC2: 'Reply on RC2', Soufiane Karmouche, 07 Feb 2024

Peer review completion

AR: Author's response | RR: Referee report | ED: Editor decision | EF: Editorial file upload
ED: Reconsider after major revisions (12 Feb 2024) by Gabriele Messori
AR by Soufiane Karmouche on behalf of the Authors (27 Feb 2024)  Author's response   Author's tracked changes   Manuscript 
ED: Referee Nomination & Report Request started (01 Mar 2024) by Gabriele Messori
RR by Anonymous Referee #1 (04 Mar 2024)
ED: Publish subject to technical corrections (07 Apr 2024) by Gabriele Messori
AR by Soufiane Karmouche on behalf of the Authors (29 Apr 2024)  Manuscript 

Journal article(s) based on this preprint

11 Jun 2024
Changing effects of external forcing on Atlantic–Pacific interactions
Soufiane Karmouche, Evgenia Galytska, Gerald A. Meehl, Jakob Runge, Katja Weigel, and Veronika Eyring
Earth Syst. Dynam., 15, 689–715, https://doi.org/10.5194/esd-15-689-2024,https://doi.org/10.5194/esd-15-689-2024, 2024
Short summary
Soufiane Karmouche, Evgenia Galytska, Gerald A. Meehl, Jakob Runge, Katja Weigel, and Veronika Eyring
Soufiane Karmouche, Evgenia Galytska, Gerald A. Meehl, Jakob Runge, Katja Weigel, and Veronika Eyring

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Short summary
This study explores Atlantic-Pacific interactions and their response to external factors. Using advanced causal analysis, we analyzed climate data from 1950–2014, revealing a shift from a Pacific- to an Atlantic-driven regime. The contrasting impacts between El Niño and Tropical North Atlantic temperatures were highlighted, along with different pathways connecting the two oceans. These findings have the potential to enhance understanding of the climate system and guide model improvements.