Further improvements to limited area mode for ICON-O

The Earth System Modelling at the Weather Scale (ESM-W) project, a collaboration between the German Weather Service (DWD) and GeoInfoDienst BW, aims to develop a coupled ocean-atmosphere forecasting system. This system will utilize the ICON-O ocean model developed by Max-Planck-Institute for Meteorology (MPI-M) and the ICON-NWP atmospheric model developed by the DWD.

 

As part of the project, a regional variant (limited area mode) of ICON-O model has been developed with the support of MPI-M. The ICON-O-LAM model takes the boundary and initial data from a previously ran coarser global simulation. The source of the data is not predefined, so users are free to choose whatever they like, as long as all needed variables are present in the dataset. The main advantage of this model is its quickness compared to same-resolution global models, due to its smaller domain size. It also has, therefore, much lower memory and compute requirements.

 

We present the state of our model, which received some improvements, based on the regional atmospheric model at the DWD and suggestions from the MPI-M. The first of them is better support for coupling between ICON-O-LAM (ocean model) and ICON-LAM (atmospheric model) which was previously only technically possible. This means the coupling criteria are now well defined and verified during the runtime. The second one is new file storage optimization by utilizing boundary grids for storing lateral boundary data. This results in much leaner file sizes for the boundary datasets. The third improvement is adding the option to use standard z coordinate system, which was available in the global ICON-O model for a long time and is interesting for some use cases. Finally, the fourth improvement is an IO optimization, where simulation times are reduced by using dedicated processors and asynchronously reading the boundary data.