Simplified version of the LMDZ atmospheric general circulation model

LMDZE is a fork of LMDZ. The fork dates from revision 691 of LMDZ in April 2006. Note that that was the time just before LMDZ was parallelized. Since then, LMDZE has evolved mostly in form and very little in content. So, essentially, the content of LMDZE is the content of LMDZ that was used for CMIP3 (or, equivalently, AR4). Actually, the content is even simpler than the CMIP3 version of LMDZ because the coupling parts of LMDZ have been removed: LMDZE can only be used with forced ocean and sea ice, without Orchidée. In form, LMDZE has evolved aiming at clarity and robustness of the source code, taking advantage of modern features of the Fortran language.

What makes the code of an atmospheric general circulation model ("GCM") complex and hard to understand? Many things. The physical parameterizations and the numerical schemes for solving partial differential equations may be complex by themselves. If your main interest is in following and understanding physical parameterizations and numerical schemes, it is a great help to eliminate other sources of complexity. Experience shows that parallelism and coupling with other models bring a code to a whole new level of darkness. Another constraint that real GCMs have and that significantly weighs on their clarity is that they must be very careful about backward compatibility. This means the code becomes loaded with very little-used options, branchings and alternate versions of subroutines. So LMDZE breaks free of all this: no parallelism, no coupling, freedom to eliminate stale code. What remains is a working GCM that is still close in structure to LMDZ, much simpler to read, and can thus be used to understand what is going on in LMDZ, or, more generally, what is in a GCM. Also, LMDZE is a test of ideas on the best architecture for a large code in modern Fortran.

Dependencies: CMake (version ≥ 3.16), XIOS, the NetCDF-C library, the NetCDF-Fortran library, MPI.

git clone --recurse-submodules https://github.com/lguez/LMDZE.git
cd LMDZE
mkdir build
cd build
cmake .. -DFETCH=ON \
   -DXIOS_INCLUDE_DIR=/directory/containing/XIOS/inc \
   -DXIOS_LIBRARY=/directory/containing/XIOS/lib/libxios.a
make