Published April 24, 2024 | Version 1.0.1
Model Restricted

Regional Earth system model GCOAST-AHOI v2.0 with ICON-CLM

  • 1. Helmholtz-Zentrum Hereon


GCOAST-AHOI is a subset of GCOAST that includes model components for A-Atmosphere and Land, H-Hydrological discharge, O-Ocean, and I-Sea Ice. GCOAST-AHOI version 1.0 (Ho-Hagemann et al., 2020) contains the atmospheric model CCLM v5.0 (Rockel et al., 2008), the ocean model NEMO v3.6 including the sea ice model LIM3 (Madec et al., 2017) and the hydrological discharge model HD v4.0 (Hagemann et al., 2020), coupled via OASIS3-MCT v2.0. A detailed description of CCLM, NEMO and HD as components of GCOAST-AHOI can be found in Ho-Hagemann et al. (2020).
In the GCOAST-AHOI version 2.0, ICON-CLM replaces CCLM as atmospheric model, which is coupled to NEMO v3.6 and HD v5.1 via OASIS3-MCT v4.0.


ICON-CLM is the regional climate model that has been developed by the Deutscher Wetterdienst (DWD) and the Climate Limited-area Modeling Community (CLM-Community) since 2017 (Pham et al., 2021). ICON-CLM is the Climate Mode of ICON-LAM (ICON-Limited Area Mode, based on the numerical weather prediction model ICON-NWP) of the global ICON (Icosahedral Nonhydrostatic) model (Zängl et al., 2015). ICON is available to the community under a permissive open source licence (BSD-3C). One can download the newest release version at
Here we publish the version v2.6.6 including the OASIS3-MCT coupling interface to couple ICON-CLM with NEMO and HD models. Note that ICON v2.6.6 was released before the open source release of ICON. As this version still comprises 3rd party modules with a more restrictive license, we had to change the file access from public to available upon request. The tar file icon_v2.6.6.tgz can be downloaded and unpacked by “tar -xzvf icon_v2.6.6.tgz”. Details how to compile ICON with the OASIS3-MCT library on Levante can be found in Ho-Hagemann, H. T. M. (2022) [].


The NEMO source code is freely available and distributed under CeCILL license (GNU GPL compatible). To download the NEMO reference version (for now revision 3.6), you have to use subversion with the following command:

svn co

In the present package, the tar file NEMO_3.6_GCOAST_openmpi_oas4.tgz includes the NEMO v3.6 source code with the settings on Levante provided in /ARCH and the compiling options in /CONFIG. In addition, we publish the extra part of source code NEMOv3.6_extras_tuning.tgz related to the new coupling method using state variables from ICON to calculate sensible and latent heat fluxes in NEMO. Details of the coupling method are described in a manuscript, which is currently prepared and will be submitted to the GMD journal.

The script in the directory CONFIG/ of the NEMO source code can be used to compile NEMO to obtain the configuration TFa2o_avg_HD_crban_tuning.


HD source code is available at The file Fopts_openmpi_levante in should be copied to the directory code/ of the HD source code with the name Fopts.


The source code of the OASIS3-MCT (Valcke et al., 2015) can be downloaded from
Source code of OASIS3-MCT v4.0 with small modifications in lib/psmile/src/GPTLget_memusage.c and lib/mct/mct/m_AttrVectComms.F90 is provided in the tar file oasis3-mct.tgz.

Install and running

The file provides an instruction to install model components on Levante (DKRZ), and conduct simulations with GCOAST-AHOI v2.0 using the SPICE package (Rockel and Geyer, 2022, Zenodo and the provided file icpl266_tuning.tgz.

Untar the file prepare_input.tgz one will obtain a package which can be used to prepare all input files as provided in OASIS_input.tgz. Two tar files eval.tgz and Rplot.tgz comprise some shell scripts and R scripts for the evaluation.


  • Hagemann, S., T. Stacke and H.T.M. Ho-Hagemann, High resolution discharge simulations over Europe and the Baltic Sea catchment. Front. Earth Sci., 8:12., 2020.
  • Hagemann, S., and Ho-Hagemann, H.T.M.: The Hydrological Discharge Model - a river runoff component for offline and coupled model applications (5.1.0). Zenodo., 2021
  • Ho-Hagemann, H. T. M., Hagemann, S., Grayek, S., Petrik, R., Rockel, B., Staneva, J., Feser, F., and Schrum, C.: Internal model variability in the regional coupled system model GCOAST-AHOI, Atmosphere, 11, 227,, 2020.
  • Ho-Hagemann, H. T. M. (2022). The OASIS3-MCT Coupling Interface for ICON-CLM (1.0.0). Zenodo.
  • Madec, G., Bourdallé-Badie, R., Bouttier, P.-A., Bricaud, C., Bruciaferri, D., Calvert, D., Chanut, J., Clementi, E., Coward, A., Delrosso, D., Ethé, C., Flavoni, S., Graham, T., Harle, J., Iovino, D., Lea, D., Lévy, C., Lovato, T., Martin, N., Masson, S., Mocavero, S., Paul, J., Rousset, C., Storkey, D., Storto, A., and Vancoppenolle, M.: NEMO ocean engine (Version v3.6-patch), Tech. rep., Pôle De Modélisation De L’institut Pierre-simon Laplace (IPSL), Zenodo,, 2017.
  • Pham, T. V., Steger, C., Rockel, B., Keuler, K., Kirchner, I., Mertens, M., Rieger, D., Zängl, G., and Früh, B.: ICON in Climate Limited-area Mode (ICON release version 2.6.1): a new regional climate model, Geosci. Model Dev., 14, 985–1005,, 2021.
  • Rockel, B., and Geyer, B. (2022). SPICE (Starter Package for ICON-CLM Experiments) (2.1). Zenodo.
  • Rockel, B., Will, A., and Hense, A.: The regional climate model COSMO-CLM (CCLM), Meteorol. Z. 2008, 17, 347–348. doi:10.1127/0941-2948/2008/0309, 2008.
  • Valcke, S.; Craig, T.; Coquart, L. OASIS3-MCT user guide, OASIS3-MCT 3.0. Technical Report TR/CMGC/15/38, CERFACS, Toulouse, France, CERFACS/CNRS SUC URA No 1875, 2015


I appreciate the technical support from Irina Fast and Panagiotis Adamidis (DKRZ). I thank Daniel Rieger and Daniel Reinert (DWD) for their support in clarifying questions regarding the handling of variables in ICON-NWP. I would like to express my thanks to Burkhardt Rockel (Hereon, retired) and Beate Geyer (Hereon) for the Starter Package for ICON-CLM Experiments (SPICE) which is helpful to conduct experiments with ICON-CLM.

Copyright and License


Copyright © 2021 Institute of Coastal Systems - Analysis and Modelling, Helmholtz-Zentrum Hereon
Licensed under the BSD-3C License (see file in

Note that ICON v2.6.6 was released before the open source release of ICON. As this version still comprises 3rd party modules with a more restrictive license, we had to change the file access from public to available upon request.

Author: Ha Thi Minh Ho-Hagemann

Contact: Ha Hagemann, Helmholtz-Zentrum Hereon, Email:

Contributors: Sebastian Grayek (formerly at Helmholtz-Zentrum Hereon); Stefan Hagemann (Helmholtz-Zentrum Hereon); Stefan Poll (Forschung Zentrum Jülich, FZJ); Vera Maurer (DWD)

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.



The record is publicly accessible, but files are restricted to users with access.