Canonical System Configurations (CSC)
Article published on 15 July 2021
last modification on 27 October 2021

by pottier
Operational CSC at ACCORD Partners

The NWP codes shared and developed in ACCORD use, to some extent, the IFS/ARPEGE global codes as backbone. Additional codes, not directly related to IFS/ARPEGE, are needed to form a full ACCORD model executable file (SURFEX surfaces cheme, Méso-NH physics package, specific surface assimilation codes etc.).

The full ACCORD NWP system is currently being developed along 3 main model configurations,the so-called Canonical System Configurations (“CSC”):

The operational CSC running at ACCORD Partners are described in the article about operational configurations.

The aim in ACCORD is to progressively make a transition towards fully transversal, CSC-agnostic system configurations. This so-called “convergence” should be achieved by reaching a high degree of interoperability across the CSCs on various aspects such as physics, components of DA and EPS, scripting, and quite notably a common working environment and common work practice.

ACCORD codes are regularly updated with new R&D developments, technical code overhauls and phasing with the IFS/ARPEGE backbone codes. This evolution leads to the definition of new releases over time, aka as T-cycles. T-cycles are regularly defined by the successful integration and validation of code developments from the different partners (in ACCORD, including Météo-France contributions, and impact of the IFS/ARPEGE code changes on the LAM components when relevant).

The code evolution process is currently undergoing a modernization in terms of work environment, process and tools.The aim in ACCORD is to move to an incremental code integration with systematic evaluation of non-regression (of existing testing configurations), reproducibility of numerical results (unless otherwise stated by a contributor), new tests when appropriate. The intention is furthermore to make use of modern code configurations (e.g. like available with OOPS) and new testing tools (e.g. “DAVAÏ” [1]). All model configurations are addressed in the test procedure (ie IFS, ARPEGE and the LAMs).

The efforts devoted for code and system maintenance in ACCORD are described in the yearly updated Rolling Work Plan and their staffing is regularly being reported (by the local teams) and monitored (by the Programme Management).

Main Harmonie-Arome publications:

  • Forecast model: Bengtsson, L., et al., 2017. “The Harmonie-Arome model configuration in the ALADIN-HIRLAM NWP System”, MWR 145, pp.1919-1935 ,
  • Data assimilation system: Gustafsson, N., et al., 2018. “Survey of data assimilation methods for convective-scale numerical weather prediction at operational centers”, QJRMS,2018,
  • 4D-Var: Jan Barkmeijer , Magnus Lindskog, Nils Gustafsson, Jelena Bojarova, Roohollah Azad, Isabel Monteiro, Pau Escribà, Eoin Whelan, Martin Ridal, Jana Sánchez-Arriola, Ole Vignes, Roel Stappers, Roger Randriamampianina, 2021: HARMONIE-AROME 4D-Var. ALADIN-HIRLAM Newsletter 16, p.20,
  • HarmonEPS: Frogner, I., U. Andrae, J. Bojarova, A. Callado, P. Escribà, H. Feddersen, A. Hally, J. Kauhanen, R. Randriamampianina, A. Singleton, G. Smet, S. van der Veen, and O. Vignes, 2019: HarmonEPS—The HARMONIE Ensemble Prediction System. Wea. Forecasting, 34, 1909–1937,
  • HCLIM: Belušić, D., de Vries, H., Dobler, A., Landgren, O., Lind, P., Lindstedt, D., Pedersen, R. A., Sánchez-Perrino, J. C., Toivonen, E., van Ulft, B., Wang, F., Andrae, U., Batrak, Y., Kjellström, E., Lenderink, G., Nikulin, G., Pietikäinen, J.-P., Rodríguez-Camino, E., Samuelsson, P., van Meijgaard, E., and Wu, M.: HCLIM38: a flexible regional climate model applicable for different climate zones from coarse to convection-permitting scales, Geosci. Model Dev., 13, 1311–1333,, 2020.