Journal cover Journal topic
Geoscientific Model Development An interactive open-access journal of the European Geosciences Union
Geosci. Model Dev., 10, 1549-1586, 2017
https://doi.org/10.5194/gmd-10-1549-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Model description paper
13 Apr 2017
The COSMO-CLM 4.8 regional climate model coupled to regional ocean, land surface and global earth system models using OASIS3-MCT: description and performance
Andreas Will1, Naveed Akhtar2, Jennifer Brauch3, Marcus Breil4, Edouard Davin5, Ha T. M. Ho-Hagemann6, Eric Maisonnave7, Markus Thürkow8, and Stefan Weiher1 1Institute for Environmental Sciences, BTU Cottbus-Senftenberg, Germany
2Institute for Atmospheric and Environmental Sciences, Goethe University, Frankfurt am Main, Germany
3Deutscher Wetterdienst, Offenbach am Main, Germany
4Institute of Meteorology and Climate Research, KIT, Karlsruhe, Germany
5Institute for Atmospheric and Climate Science, ETH, Zurich, Switzerland
6Institute of Coastal Research, Helmholtz-Center Geesthacht, Germany
7Centre Européen de Recherche et de Formation Avancée en Calcul Scientifique, CERFACS-CNRS,Toulouse, France
8Institute of Meteorology, FU Berlin, Germany
Abstract. We developed a coupled regional climate system model based on the CCLM regional climate model. Within this model system, using OASIS3-MCT as a coupler, CCLM can be coupled to two land surface models (the Community Land Model (CLM) and VEG3D), the NEMO-MED12 regional ocean model for the Mediterranean Sea, two ocean models for the North and Baltic seas (NEMO-NORDIC and TRIMNP+CICE) and the MPI-ESM Earth system model.

We first present the different model components and the unified OASIS3-MCT interface which handles all couplings in a consistent way, minimising the model source code modifications and defining the physical and numerical aspects of the couplings. We also address specific coupling issues like the handling of different domains, multiple usage of the MCT library and exchange of 3-D fields.

We analyse and compare the computational performance of the different couplings based on real-case simulations over Europe. The usage of the LUCIA tool implemented in OASIS3-MCT enables the quantification of the contributions of the coupled components to the overall coupling cost. These individual contributions are (1) cost of the model(s) coupled, (2) direct cost of coupling including horizontal interpolation and communication between the components, (3) load imbalance, (4) cost of different usage of processors by CCLM in coupled and stand-alone mode and (5) residual cost including i.a. CCLM additional computations.

Finally a procedure for finding an optimum processor configuration for each of the couplings was developed considering the time to solution, computing cost and parallel efficiency of the simulation. The optimum configurations are presented for sequential, concurrent and mixed (sequential+concurrent) coupling layouts. The procedure applied can be regarded as independent of the specific coupling layout and coupling details.

We found that the direct cost of coupling, i.e. communications and horizontal interpolation, in OASIS3-MCT remains below 7 % of the CCLM stand-alone cost for all couplings investigated. This is in particular true for the exchange of 450 2-D fields between CCLM and MPI-ESM. We identified remaining limitations in the coupling strategies and discuss possible future improvements of the computational efficiency.


Citation: Will, A., Akhtar, N., Brauch, J., Breil, M., Davin, E., Ho-Hagemann, H. T. M., Maisonnave, E., Thürkow, M., and Weiher, S.: The COSMO-CLM 4.8 regional climate model coupled to regional ocean, land surface and global earth system models using OASIS3-MCT: description and performance, Geosci. Model Dev., 10, 1549-1586, https://doi.org/10.5194/gmd-10-1549-2017, 2017.
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Short summary
We present a coupled regional climate system model. The COSMO CLM regional climate model is two-way coupled via OASIS3-MCT to the land surface, regional ocean for the Mediterranean Sea, North and Baltic seas and an earth system model. The direct coupling costs of communication and horizontal interpolation are shown to be negligible even for a frequent exchange of 450 2-D fields. A procedure of finding an optimum processor configuration is presented and successfully applied to all couplings.
We present a coupled regional climate system model. The COSMO CLM regional climate model is...
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