Preprints
https://doi.org/10.5194/gmd-2023-13
https://doi.org/10.5194/gmd-2023-13
Submitted as: development and technical paper
 | 
09 Feb 2023
Submitted as: development and technical paper |  | 09 Feb 2023
Status: this preprint is currently under review for the journal GMD.

A flexible z-coordinate approach for the accurate representation of free surface flows in a coastal ocean model (SHYFEM v. 7_5_71)

Luca Arpaia, Christian Ferrarin, Marco Bajo, and Georg Umgiesser

Abstract. We propose a z-coordinate algorithm for ocean models which, thanks to the insertion and removal of surface layers, can deal with an arbitrarily large tidal oscillation independently of the vertical resolution. The algorithm is based on a classical two steps procedure used in numerical simulations with moving boundaries (grid movement followed by a grid topology change, that is insertion/removal of surface layers) which leads to a stable and accurate numerical discretization. With ad-hoc treatment of advection terms at non-conformal edges that may appear due to insertion/removal operations, mass conservation and tracer constancy are preserved. This algorithm, called z-surface-adaptive, can be reverted, as a particular case when all layers are moving, to other z-surface-following coordinates, such as z-star or quasi-z. With simple analysis and realistic numerical experiments, we compare the surface-adaptive-z coordinate against z-star and we show that it can be used to simulate effectively coastal flows with wetting and drying.

Luca Arpaia et al.

Status: open (until 06 Apr 2023)

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  • RC1: 'Comment on gmd-2023-13', L. Bonaventura, 08 Mar 2023 reply

Luca Arpaia et al.

Model code and software

SHYFEM version with z-surface-adaptive coordinates Luca Arpaia https://doi.org/10.5281/zenodo.7528682

Luca Arpaia et al.

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Short summary
We propose a z-coordinate vertical algorithm for coastal ocean models which, thanks to the insertion and removal of surface layers, can deal with an arbitrarily large tidal oscillation, independently of the vertical resolution, in a stable and accurate fashion. With simple analysis and realistic numerical experiments we show that it can be used to simulate effectively coastal flows with wetting and drying.