ICON Mesh Splitter version 1.1 - A program to create irregular computational meshes for ICON-O

Icon Mesh Splitter (IMS) is a simple Linux console tool for generating meshes for the ICON-O ocean model
(Korn et al. 2022). The resulting NetCDF mesh file can be read and used directly by ICON-O.
In this version of the program, only global grids are generated. These are based on the ETOPO1 topography
(Amante & Eakins 2009) with manipulated values in the area of the southeastern North Sea to obtain a more
accurate land-sea mask.

The other base is the icosahedron, a polyhedron formed by 20 equilateral triangles. This rather coarse
global mesh is refined using the bisectional method. Here, 3 new vertices are introduced at half the length
of the 3 sides of the triangle. If these three new vertices are connected by three new sides, 4 new equilateral
triangles are created from the old triangle.

IMS always starts with a uniform icosahedral grid of the global sphere with a resolution of about 160 km.
This grid is created by a fivefold bisectional refinement of the original 20 sided icosahedron.
The number of cells in this grid is therefore 20*4*4*4*4*4 = 20480. This grid, with removed land cells, is the
first mesh that the IMS offers, if the user does not wish to refine it further.

However, the user must define a global matrix of the desired grid refinements using a so-called "levelmap".
With this, IMS can be instructed to refine the grid only regionally, and thus generates an irregular grid.

In addition, the user can activate "coastal refinement" for the different refinement levels.

You find more information about the mesh generation technique in Logemann et al. (2021).

Amante, C. and Eakins, B.W. (2009). ETOPO1 1 Arc-Minute Global Relief Model: Procedures, Data Sources and Analysis.
NOAA Technical Memorandum NESDIS NGDC-24. National Geophysical Data Center, NOAA. doi:10.7289/V5C8276M 

Korn, P., Brüggemann, N., Jungclaus, J. H., Lorenz, S. J., Gutjahr, O., Haak, H., et al. (2022). ICON-O: The ocean
component of the ICON Earth system model—Global simulation characteristics and local telescoping capability. Journal
of Advances in Modeling Earth Systems, 14, e2021MS002952. https://doi.org/10.1029/2021MS002952

Logemann, K., Linardakis, L., Korn, P., & Schrum, C. (2021). Global tide simulations with ICON-O: Testing the model
performance on highly irregular meshes. Ocean Dynamics, 21(1), 43–57. https://doi.org/10.1007/s10236-020-01428-7