CICE Recent Changes

Important changes to the code on the master branch since the last numbered release

Date of last update: 18 Aug 2026

By: T. Craig

Last numbered release: CICE 6.6.3 (Jan 30, 2026)

Since the last release, the directory structure of the communication infrastructure has been updated. The cicecore/cicedyn/infrastructure comm/mpi and comm/serial directories have been merged into the comm directory. A new CPP, NO_MPI, exists to support building CICE without MPI. Build systems may need to modify their build filepaths, remove comm/mpi and comm/serial and just point to the comm directory.

There are also some significant changes to support regional grids via updates to boundary conditions, boundary restoring, and interior restoring. Work on regional grid capabilities continue.

Results with calc_Tsfc=.false. have changed with a new flux limiter in Icepack. snow and bgc configuration answers have changed due to enforcement of the minimum snow grain radius. Configurations with C and CD grids have changed answers because the rheology term is now set to zero for very low ice concentrations in those cases.

Major Changes

• Update halo and interior restoring capability. This was a significant update to support regional grid features and to allow further testing and development. #1110
• Merge the infrastructure comm/mpi and comm/serial code, add CPP NO_MPI to support serial builds if MPI is not available, add gather/scatter unit tester. #1127 #1131

Bug fixes

• Updates and bug fixes for CMIP7 output #1088
• Update Icepack to enforce minimum snow grain radius. This changes answers for snow and bgc configurations. #1089
• Initialize worka for the 'sifb' history output #1092
• Set rheology term to zero for the C-grid for low concentration values at the E and N points. This changes answers for C and CD grid configurations. #1105
• Update Icepack to add conductive flux limiting for vertical thermodynamics. This changes answers for calc_Tsfc=.false. #1130
• Fix the rotation angles in MOM supergrid #1128

Enhancements

• Update derecho shared batch job submission #1091
• Add zero-gradient and linear_extrap boundary conditions #1094
• Machine port to Betzy #1098
• Remove references to no-longer-used fields #1101
• Fix datatypes in the haloUpdate code. This does not impact results. #1104
• Update derecho intel and inteloneapi ports #1107
• Update blueback port #1121
• Update carpenter port #1131
• Add mpif08 unit test #1107
• Add UFS tracing instrumentation to nuopc/cmeps driver #1075
• Fixed several minor bugs in recent implementations, all changes are bit-for-bit. Includes length of character string, removal of redundant code, setting the missing value when reading netcdf files, and uninitialized fill values #1118 #1122
• Update the plotting scripts to support box testing #1114
• Remove unused variables in source code #1126

Documentation

• Update .zenodo.json author list #1090
• Update snwredist documentation #1100
• Update forum links #1130

Important NOTES