EGU General Assembly 2021
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Design of Runge-Kutta based split-explicit time integration algorithms for the NEMO ocean model

Nicolas Ducousso1, Florian Lemarié1, Gurvan Madec1,2, and Laurent Debreu1
Nicolas Ducousso et al.
  • 1Inria, Laboratoire Jean Kuntzmann, Saint Martin d'Hères, France (
  • 2LOCEAN, Institut Pierre Simon Laplace, Paris, France

The NEMO ocean model is currently based on the Leapfrog scheme that provides a good combination between simplicity and efficiency for low-resolution global simulations. However, this scheme is subject to difficulties that question its relevance at high-resolution : the necessary damping of its computational mode, e.g. via a Robert-Asselin filter, affect stability and increases amplitude and phase errors of the physical mode ; because it is unconditionally unstable for diffusive processes, monotonicity or positive-definiteness comes at a substantial cost and complication. The evolution toward a 2-level time stepping algorithm based on Runge-Kutta schemes is studied. Special attention is given to how to articulate a mode-splitting technique to handle the fast dynamics associated with the free surface. Linear stability analyses of several Runge-Kutta based, split-explicit algorithms are performed and the most promising ones are identified. They allow a good compromise between robustness, stability and accuracy for integration of internal gravity waves, Coriolis and advection processes. Idealized test-cases illustrate the benefits associated to the revised time-stepping compared to the original Leapfrog.

How to cite: Ducousso, N., Lemarié, F., Madec, G., and Debreu, L.: Design of Runge-Kutta based split-explicit time integration algorithms for the NEMO ocean model, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9078,, 2021.


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