Changes between 4.2.2 and 4.2.1

List of the main bugfixes in the new 4.2.2 release - Dec 2023

Main bug fixes

  • Fix ice-ocean stress: (!402)

  • Fix weekly forcings: (!360)

  • Fix grazing by mesozooplankton: (!346)

  • Fix OBS operator for reproducibility: (!342)

  • makenemo improvements: (!344)

Additional bug fixes

  • Nesting tools: (!351)

  • Hard coded flags in ASM: (!367)

  • Include F-folding in DOMAINcfg tool: (!396)

  • Slight change in field_def_nemo-ice.xml: (!398)

  • Allow snow-ice formation when SST>0C: (!404)

  • Debug Richardson number vertical mixing scheme (!420)

  • Debug Langmuir cells when coupling with waves in tke (!421)

New feature

  • Addition of a 3d order upstream advection scheme alongside the “old” UBS scheme for momentum: (!349). This scheme is implemented in the new version of NEMO but cannot be compared to UBS since the latter has disappeared from the code. Hence, it has been decided to plug the 3d order upstream in version 4.2, so that comparisons with UBS can be done. It requires an additional namelist parameter (ln_dynadv_up3).

Changes since 4.2.0

List of the main bugfixes in the new 4.2.1 release - May 2023


  • Fix Reynolds number in flow dependent Laplacian (!298)

  • Fix non monotonic behavior of FCT tracer advection scheme with non-linear free surface (!292)

  • Fix emp initial value if salinity relaxation is not used (!221)

  • TKE boundary condition in GLS was wrong with iceshelves cavities (

  • Model initialization in coupled configurations fixed (!151)

  • ABL model was not working with waves options (!144)

  • Spitz 12 configuration namelists have been updated (!175)

  • Bugfixes in the OSMOSIS vertical mixing scheme and the associated diagnostics (!172, !168)

  • CPL_OASIS test case has been updated (!111)

  • Fix surface mixing length calculation in TKE scheme when using wave model Stokes drift and tiling (!302)

Sea-ice SI3

  • Surface roughness can now be ice-thickness dependant in GLS and TKE scheme (!49)

  • A bug in Rothrock ice strength has been fixed (!139)

High Performance Computing (HPC)


Several fixes have been made to the tiling introduced at 4.2.0 (ln_tile = .TRUE.), but users may still encounter bugs when using this functionality (disabled by default). Improvements to the robustness and performance of the tiling will be available with the next major release of NEMO.

  • Enable NEMO compilation using single-precision variable (!171)

  • Fix NEMO compilation when using MPI2 option (!97) and bugfix in configurations without MPI use (!167)

  • Demonstration of mixed-precision compilation using key_single (ORCA2 only) (!261)

AGRIF zooms

  • Correct freshwater budget computation when using AGRIF zooms (!162)

  • Fixed issue with sea surface height (ssh) offset with sea-ice and AGRIF (!121, !128, !149)

Tracers and biogeochemistry TOP

  • PISCES consolidation and robustness (reproducibility, bugfix corrections, memory optimisation)

  • Extension of passive-tracer conservation to the Euler-forward time-stepping option (!187) and generic accuracy of the restart mechanism for configurations with Euler-forward time integration (!96)

  • Bugfix on offline transport in TOP when using linear surface option (!141)

  • Boundary conditions were missing in 1D configurations with TOP (!103)

  • Improve the use of multiple BDY segments and tracer inputs fields within TOP (!231)

Input Output Manager

  • Enable the use of XIOS3 to create outputs and handle restart files by means of key_xios3 (!267)

  • Possibility to shift the record from the middle of the forcing period to the beginning or the end when using temporal interpolation with fldread (!311)


  • Correction of the isotherm-depth computation (!288)

  • Some dia_ar5_hst outputs were wrong (!140)

  • The qsr3d diagnostic could not be output (!296)

  • Some dia_ar5 diagnostics could not be output, and some diagnostics gave different results with tiling (!301)

  • diadct mfo/sfo/hfo transports through sections are now handled by XIOS (!299)

Changes since 4.0.7

List of the main additions to the 4.2.0 release - February 2022

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


  • 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


  • 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)


  • 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)


  • Tests cases now available with most new developments

  • SETTE validation script improvements

  • OASIS test case for ocean atmosphere coupled interface

Known Issues

  • 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 !)