NWP | ICON

ICON

• https://www.icon-model.org/

ICOsahedral Nonhydrostatic model (ICON) is a flexible, scalable, high-performance modelling framework for weather, climate and environmental prediction that provides actionable information for society and advances our understanding of the Earth's climate system.

ICON is evolving into an internationally recognized and widely used modeling framework for weather, climate, and environmental prediction that allows the users to solve challenging problems of high societal relevance. It will push the boundaries of what is computationally feasible to advance knowledge and understanding and support innovation in weather, climate and environmental services.

• The NWP System at Meteoswiss in a Nutshell | 2024
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ICON Grids: File Register

• http://icon-downloads.mpimet.mpg.de/

Reduced radiation grid

A reduced radiation grid in Numerical Weather Prediction (NWP) involves running computationally intensive radiation calculations on a coarser spatial grid than the main model grid to save significant computing power, often with minimal impact on forecast accuracy, a technique used by major centers like ECMWF and DWD (ICON model). This strategy, sometimes using specialized grids like octahedral ones, allows for faster forecasts by reducing the number of grid points where complex radiative transfer is computed, improving overall efficiency for global models.

• Morcrette, Jean-Jacques, George Mozdzynski, and Martin Leutbecher. "A reduced radiation grid for the ECMWF Integrated Forecasting System." Monthly weather review 136.12 (2008): 4760-4772.
• A new radiation scheme for the IFS
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• ecRad Overview

How it works:

• Grid Reduction: Instead of running radiation at every model grid point (e.g., TCo1279 resolution), calculations are done on a simpler, coarser grid (e.g., R95 or even coarser).
• Interpolation: Data is interpolated from the fine model grid to the coarse radiation grid for calculations, and results are then interpolated back, with sophisticated schemes handling boundaries (like coastlines) to minimize errors.
• Specialized Grids: Models might use octahedral grids (like cubic-octahedral) or other reduced Gaussian grids to optimize point distribution and efficiency.

Examples:

• ECMWF IFS: Implemented reduced radiation grids (e.g., R511 to R95) and newer schemes like ecRad to reduce costs significantly.
• ICON Model: Uses the ecRad scheme with configurable reduced radiation grids (e.g., lredgrid_phys = .true.) for substantial savings.

Installation

config

out-of-source builds

The building system of ICON supports so-called out-of-source builds. This means that you can build ICON in a directory other than the source root directory. The main advantage of this is that you can easily switch between several different configurations (each in its own build directory) of the model while working on the same source code. Hence, it is possible to introduce changes into the source code and test them with different compilers, flags and options without having to re-configure the model or copy the updated source files to other directories.

The configure script (also when called via a configure wrapper) prepares the current working directory for the following building. The particular case of the current working directory being the source root directory is called in-source configuration.

It is not allowed to mix in-source and out-of-source builds: the source directory must be cleaned ($ make distclean) from the files generated as a result of a prior in-source configuration and building before an out-of-source configuration can take place.