Overview: What is LMDZ-SACS?
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LMDZ-SACS is an offline tracer transport model, with forward, tangent linear and adjoint codes,
derived from the global circulation model (GCM) `LMDZ <https://lmdz.lmd.jussieu.fr/>`__
for the regular grid version and from `DYNAMICO <https://www.lmd.ipsl.fr/en/modelisations/dynamico-en/>`__ ,
the new dynamical core for LMDZ for the unstructured icosahedral grid.
The model is coupled with the SACS linear chemistry module.

The model grids
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LMDZ-SACS can be used on two types of grid, both at several resolutions (horizontal and vertical)

* The **regular latitude longitude grid**, composed of square cells with smaller areas at high latitudes

* The **unstructured icosahedral grid**, composed of hexagonal cells of similar area

Time resolution
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A LMDZ-SACS simulation is always one month long, from the first day of the month to the last day of the month.
Most of the dynamics and physics variables are computed once for all ahead of time with the full GCM averaged every 3 hours then saved to disk.
LMDZ-SACS reads these 3 hourly variables, called mass fluxes, from disk to compute the tracer transport.

Code parallelisation
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LMDS-SACS code is parallelized with `OpenACC <https://www.openacc.org/>`__ compiler directives (similar to OpenMP directive),
to be compiled for use on GPU, but can also be compiled for use on multicore CPU with some compilers.