Preprints
https://doi.org/10.5194/egusphere-2023-50
https://doi.org/10.5194/egusphere-2023-50
 
23 Jan 2023
23 Jan 2023
Status: this preprint is open for discussion.

Factors influencing the meridional width of the equatorial deep jets

Swantje Bastin1,a, Martin Claus1,2, Richard J. Greatbatch1,2, and Peter Brandt1,2 Swantje Bastin et al.
  • 1GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, Germany
  • 2Kiel University, Kiel, Germany
  • anow at: Max Planck Institute for Meteorology, Hamburg, Germany

Abstract. Equatorial Deep Jets (EDJ) are vertically alternating, stacked zonal currents that flow along the equator in all three ocean basins at intermediate depth. Their structure can be described quite well by the sum of high baroclinic mode equatorial Kelvin and Rossby waves. However, the EDJs' meridional width is larger by a factor of 1.5 than inviscid theory predicts for such waves. Here, we use a set of idealised model configurations representing the Atlantic Ocean to investigate the contributions of different processes to the enhanced EDJ width. Corroborated by the analysis of shipboard velocity sections, we show that instantaneous widening of the EDJ by irreversible mixing processes contributes more to their enhanced time mean width than averaging over meandering of the jets. Most of the widening due to meandering can be attributed to the strength of intraseasonal variability in the jets' depth range, suggesting that the jets are meridionally advected by intraseasonal waves. Only a weak connection to intraseasonal variability is found for the EDJs' instantaneous widening, corroborating and connecting earlier theories that any process dissipating the EDJs' momentum would broaden them, but that intraseasonal variability maintains, not dissipates, the EDJ.

Swantje Bastin et al.

Status: open (until 20 Mar 2023)

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Swantje Bastin et al.

Data sets

Supplementary dataset and scripts to Bastin et al.: Factors influencing the meridional width of the equatorial deep jets (submitted to Ocean Science) Swantje Bastin, Martin Claus, Richard J. Greatbatch, Peter Brandt https://doi.org/10.5281/zenodo.7535588

Swantje Bastin et al.

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Short summary
Equatorial deep jets are ocean currents that flow along the equator in the deep oceans. They are relevant for oxygen transport and tropical surface climate, but their dynamics are not yet entirely understood. We investigate different factors leading to the jets being broader than theory predicts. Mainly using an ocean model, but corroborating the results with shipboard observations, we show that dissipation of momentum is the main factor for the broadening, but that meandering also contributes.