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Changes since 4.0.7
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List of the main additions to the new 4.2.0 release - February 2022

This section is an overview of the major NEMO upgrades as included in the new 4.2.0 release. 

If you are willing to port an existing configuration in order to start using this new release, it is sugggested to also look at the 4.2 `Migration Guide`_ .

.. _`Migration guide`: https://sites.nemo-ocean.io/user-guide/migration.html

**KERNEL**

- New vertical scale factors management (improving computational performance and reducing memory footprint) via added keys: 
   - key_qco (Quasi Eulerian Coordinates) 
   - key_linssh (Linear Sea Surface Height)
- New HPG schemes (improvements and new option)
- Preparatory stages for new RK3 time stepping scheme, includes: 
   - time-pointer changes
   - DO LOOP macros
   - changes in main arrays dimensions)
- Full Shallow Water setup

**AIR SEA INTERACTIONS**

- Currents feedbacks
- Mass-flux convection scheme (still not compatible with TOP & PISCES)
- Bulk improvements 
- Atmospheric Boundary layer model (1D vertical as for now) & tools improvements
- Wave forcing improvements

**AGRIF zooms**

- Improvement of Agrif for global configurations (periodic, north fold zoom, HPC), 
- Allow AGRIF for multiple vertical grids
- Updated Nesting Tools to set up the AGRIF zooms

**Sea-ice SI3**

- EAP & VP rheology (V&V to complete)
- Melt ponds (preliminary implementation)
- (Updated Reference Manual will be made available to users by March 2022)

**ENHANCEMENTS**

- Ocean column properties in NEMO-ICB
- OSMOSIS (awaiting improvements)
- Update internal tidal mixing 

**Tracers and biogeochemistry TOP**

- Ice sheet iron sources
- Scheme for vertical penetration of visible light
- (Updated Reference Manual will be made available to users by March 2022)

**DATA interface**

- OBS modifications

**Input Output Manager**

- Use XIOS to read & write restart file (allowing to produce a unique restart file while using domain decomposition)

**High Performance Computing (HPC)**

- MPI Communication cleanup & improvements using MPI3
- Reduction in memory footprint
- Improved computational performance of solar penetration scheme
- Additional improvements in preparation (requiring further developments before producing performance gains):
   - Extra Halo extension (namelist activation but keep nn_hls=1 for now)
   - Mixed precision preparatory phase
   - Loop fusion (activated via key_loop_fusion not currently recommended)
   - Tiling (namelist activation but keep ln_tile=.false. for now)

**VERIFICATION & VALIDATION**

- Tests cases now available with most  new developments
- SETTE validation script improvements
- OASIS test case for ocean atmosphere coupled interface


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Known Issues
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- Simulations are not reproductible when using a halo size of 2 points (MR !34 for details)
- Domain attributes are missing in multiple file output (Issue #14)
- SI3 manual is not yet available (coming soon !)