Preprints
https://doi.org/10.5194/os-2021-30
https://doi.org/10.5194/os-2021-30

  20 Apr 2021

20 Apr 2021

Review status: this preprint is currently under review for the journal OS.

Flow separation, dipole formation and water exchange through tidal strait

Ole Anders Nøst1,3 and Eli Børve2,4 Ole Anders Nøst and Eli Børve
  • 1Akvaplan-niva AS, 7462 Trondheim, Norway
  • 2The University of Oslo, Department of Geosciences, 0315 Oslo, Norway
  • 3Nord University, 8026 Bodø, Norway
  • 4Akvaplan-niva AS, 9296 Tromsø, Norway

Abstract. We investigate the formation and evolution of dipole vortices and their contribution to water exchange through idealized tidal straits. Self-propagating dipoles are important for transporting and exchanging water properties through straits and inlets in coastal regions. In order to obtain a robust data-set to evaluate flow separation, dipole formation and evolution and the effect on water exchange, we conduct 164 numerical simulations, varying the width and length of the straits as well as the tidal forcing. We show that dipoles are formed and start propagating at the time of flow separation, and their vorticity originates in the velocity front formed by the separation. We find that the dipole propagation velocity is proportional to the tidal velocity amplitude, and twice as large as the dipole velocity derived for a dipole consisting of two point vortices. We analyse the processes creating a net water exchange through the straits and derive a kinematic model dependent on dimensionless parameters representing strait length, dipole travel distance and dipole size. The net tracer transport resulting from the kinematic model agrees closely with the numerical simulations and provide understanding of the processes controlling net water exchange.

Ole Anders Nøst and Eli Børve

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on os-2021-30', Anonymous Referee #1, 11 May 2021
    • AC2: 'Reply on RC1', Ole Anders Nøst, 04 Jun 2021
  • RC2: 'Comment on os-2021-30', Anonymous Referee #2, 13 May 2021
    • AC1: 'Reply on RC2', Ole Anders Nøst, 01 Jun 2021
  • RC3: 'Comment on os-2021-30', Anonymous Referee #3, 24 May 2021
    • AC3: 'Reply on RC3', Ole Anders Nøst, 01 Jul 2021

Ole Anders Nøst and Eli Børve

Ole Anders Nøst and Eli Børve

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Short summary
Narrow tidal strait often leads to net transport in one direction, and the water flowing through the strait is not the same is the water that is drawn back into the strait when the tidal flow turns. We have investigated this process by simulating the transport through tidal straits of different lengths and widths. A simple theory is established that describes the net transport. The theory can be applied to real coastlines when predicting spreading of pollution and other substances in the ocean.