On the dynamics of an idealised bottom density current overflowing in a semi-enclosed basin: mesoscale and submesoscale eddies generation

Abstract

The Red Sea Water enters the Gulf of Aden through the Strait of Bab El Mandeb as a density current. The Red Sea Water subsequently spreads into the Gulf of Aden under the influence of surface mesoscale eddies, which dominate the surface flow, of topographic features such as rift and capes, and of the monsoon regimes. The dynamics of a bottom density current overflowing in a semi-enclosed basin, as the Red Sea Water outflows in the Gulf of Aden, is investigated by performing idealised numerical simulations, at submesoscale resolution, in which we progressively add topographic and dynamical elements. The rift and cape play an important role, respectively, on the vertical and the horizontal mixing as well as baroclinic and barotropic instabilities undergone by the bottom density current. Mesoscale and submesoscale eddies are generated depending on the model configuration. In the presence of surface mesoscale eddies, the bottom density current water is mainly advected at their periphery. In winter, both mesoscale and submesoscale eddies are generated, while in summer only submesoscale eddies are present. Finally, to put our results based on idealised numerical simulations and Lagrangian experiments in perspective, we analyse the trajectories of three Argo floats, deployed in the Rift of Tadjurah. Clues of submesoscale eddies generation at capes are observed which is in agreement with our idealised numerical simulations.

Keywords:

• Bottom density current
• Red Sea outflow
• submesoscale eddies
• current instability
• mesoscale eddies

Acknowledgements

We acknowledge support from UBO and SHOM. The simulations were performed using the HPC resources from DATARMOR of “Pôle de Calcul Intensif pour la Mer” at Ifremer, Brest, France. MM designed and performed the numerical experiments. MM and XC analysed the results and wrote the manuscript. PLH, CdM, SC, and SL contributed to the writing of the manuscript. XC, SL, SC, PLH, CdM and MM contributed to the Argo floats deployment program.

Data availability

Model outputs are available upon request. Argo floats data are available online at https://fleetmonitoring.euro-argo.eu/dashboard.

Disclosure statement

No potential conflict of interest was reported by the author(s).