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Geoscientific Model Development An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/gmd-2020-202
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/gmd-2020-202
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: model evaluation paper 25 Aug 2020

Submitted as: model evaluation paper | 25 Aug 2020

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This preprint is currently under review for the journal GMD.

Comparison of ocean vertical mixing schemes in the Max Plank Institute Earth System Model (MPI-ESM1.2)

Oliver Gutjahr1, Nils Brüggemann1,2, Helmuth Haak1, Johann H. Jungclaus1, Dian A. Putrasahan1, Katja Lohmann1, and Jin-Song von Storch1,3 Oliver Gutjahr et al.
  • 1Max Planck Institute for Meteorology, Hamburg, Germany
  • 2University of Hamburg, Hamburg, Germany
  • 3Center for Earth System Research and Sustainability (CEN), University of Hamburg, Germany

Abstract. We compare the effects of four different ocean vertical mixing schemes on the ocean mean state simulated by the Max Planck Institute Earth System Model (MPI-ESM1.2) in the framework of the Community Vertical Mixing (CVMix) library. Besides the PP and KPP scheme, we implemented the TKE scheme and a recently developed prognostic scheme for internal wave energy and its dissipation (IDEMIX) to replace the often assumed constant background diffusivity in the ocean interior. We analyse in particular the effects of IDEMIX on the ocean mean state, when combined with TKE (TKE+IDEMIX).

In general, we find little sensitivity of the ocean surface, but considerable effects for the interior ocean. Overall, we cannot classify any scheme as superior, because they modify biases that vary by region or variable, but produce a similar pattern on the global scale.

However, using a more realistic and energetically consistent scheme (TKE+IDEMIX) produces a more heterogeneous pattern of vertical diffusion, with lower diffusivity in deep and flat-bottom basins and elevated turbulence over rough topography. In addition, TKE+IDEMIX improves the circulation in the Nordic Seas and Fram Strait, thus reducing the warm bias of the Atlantic water (AW) layer in the Arctic Ocean to a similar extent as has been demonstrated with eddy-resolving ocean models.

We conclude that although shortcomings due to model resolution determine the global-scale bias pattern, the choice of the vertical mixing scheme may play an important role for regional biases.

Oliver Gutjahr et al.

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Oliver Gutjahr et al.

Oliver Gutjahr et al.

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Short summary
We compare four ocean vertical mixing schemes in 100-year long coupled simulations with the Max Planck Institute Earth System Model (MPI-ESM1.2) and analyse their model biases. Overall, the mixing schemes modify biases in the ocean interior that vary with region and variable, but produce a similar global bias pattern. We therefore cannot classify any scheme as superior, but conclude that the chosen mixing scheme may be important for regional biases.
We compare four ocean vertical mixing schemes in 100-year long coupled simulations with the Max...
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