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Do We Require Adiabatic Dissipation Schemes in Eddy-Resolving Ocean Models?

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  • 1 Hadley Centre for Climate Prediction and Research, Meteorological Office, Bracknell, United Kingdom
  • | 2 Department of Meteorology, University of Reading, Reading, United Kingdom
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Abstract

Use of horizontal diffusion of temperature and salinity in numerical ocean models causes spurious diapycnal transfers—the “Veronis effect”—leading to erosion of the thermocline and reduced poleward heat transports. The authors derive a relation between these diapycnal transfers and the dissipation of vorticity gradients. An increase in model resolution does not significantly reduce the diapycnal transfers since vorticity gradients cascade to smaller scales and must ultimately be dissipated to maintain numerical stability. This is confirmed in an idealized primitive equation ocean model at a variety of resolutions between 1° and 1/8°.

Thus, the authors conclude that adiabatic dissipation schemes are required, even in eddy-resolving ocean models. The authors propose and implement a new biharmonic form of the Gent and McWilliams scheme, which adiabatically dissipates at the grid scale while preserving larger-scale features.

Corresponding author address: Dr. Malcolm J. Roberts, Hadley Centre for Climate Prediction and Research, Meteorological Office, Room H022, London Road, Bracknell, Berkshire RG12 2SY, United Kingdom.

Email: mjroberts@meto.gov.uk

Abstract

Use of horizontal diffusion of temperature and salinity in numerical ocean models causes spurious diapycnal transfers—the “Veronis effect”—leading to erosion of the thermocline and reduced poleward heat transports. The authors derive a relation between these diapycnal transfers and the dissipation of vorticity gradients. An increase in model resolution does not significantly reduce the diapycnal transfers since vorticity gradients cascade to smaller scales and must ultimately be dissipated to maintain numerical stability. This is confirmed in an idealized primitive equation ocean model at a variety of resolutions between 1° and 1/8°.

Thus, the authors conclude that adiabatic dissipation schemes are required, even in eddy-resolving ocean models. The authors propose and implement a new biharmonic form of the Gent and McWilliams scheme, which adiabatically dissipates at the grid scale while preserving larger-scale features.

Corresponding author address: Dr. Malcolm J. Roberts, Hadley Centre for Climate Prediction and Research, Meteorological Office, Room H022, London Road, Bracknell, Berkshire RG12 2SY, United Kingdom.

Email: mjroberts@meto.gov.uk

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