2026.07.1 - MetOffice/simulation-systems GitHub Wiki

Simulation Systems 2026.07.1 Release

Release date: 10th July 2026

Included Releases

Software Stack Updates

Upgrading a branch to the release

In order to merge the release changes from stable into your branch in your fork:

  1. Synchronise your fork with the latest changes on stable
  2. Fetch the latest changes into your clone git fetch origin
  3. Merge those changes into your branch git switch <branch name> git merge origin/stable

Alternatively, cut a new branch from stable and merge your original branch into this.

For more details see Updating Branches

LFRic Apps Key Changes

  • Addition of conservative diffusion operator for scalars (MetOffice/lfric_apps#378)
  • Ensure moisture conservation from Gungho linear solver (MetOffice/lfric_apps#394)
  • Improved representation of orography (MetOffice/lfric_apps#180)
  • Fix issues with threading and cross-panel partitions (MetOffice/lfric_apps#458)
  • Change the way lfric_atm code accesses some configuration options (MetOffice/lfric_apps:#418). See the lfric_core section for details about the linked lfric_core ticket. Note: This change may cause significant conflicts with older branches.

lfric_atm Rank / Partition Count constraint

A new constraint has been introduced into lfric_atm related to how output jobs using xios_server.exe are handled with number of ranks.

The constraint is under investigation to discover causes and explore whether it can be removed in the future.

The constraint it that the number of mpi_parts_xios must be able to exactly divide the number of faces and edges of the mesh.

The failure mode is a runtime failure, leading to a core dump, which describes memory access errors on xios_server.exe processes, e.g. <error reading variable: Cannot access memory at address 0x1e11d8>

To avoid this failure mode, it is necessary to constrain the mpi_parts_xios by analysing the mesh parameters.

! Planar
nfaces_pl = nx * ny
nedges_pl = 2*(nx*ny) + nx + ny
nnodes+pl = (nx+1) * (ny+1)

! Cubed-sphere
nfaces_cu = 6*(nx * ny)
nedges_cu = 2 * (6*nx*ny + nx - ny) 
nnodes_cu = 6*nx*ny + 2*nx - 2*ny + 2
! If nx=ny (like for all our Cn cubed-sphere meshes), this simplifies to: 
nfaces_cu = 6*n*n
nedges_cu = 2 * (6*n*n) 
nnodes_cu = 6*n*n + 2

For example, for a regional model, ral3-ukv, then the mesh is defined by: https://github.com/MetOffice/lfric_apps/blob/main/rose-stem/app/mesh/opt/rose-app-ukv_MG.conf#L17

  • 960 x 1024
    • nfaces = 960 x 1024 = 983040
    • nedges = 2 x (960 x 1024) + 960 + 1024 = 1968064
  • the largest common factor (largest common divisor) of 1968064 & 983040 is 64
  • mpi_parts_xios is set to 64 for this model configuration, to enable it to run

LFRic Core Key Changes

  • Add new coordinate space options (MetOffice/lfric_core#238)
  • Fix issues with threading and cross-panel partitions (MetOffice/lfric_core#349)
  • Most namelist configuration choices are now obtained by accessing the config object held in modeldb rather than by using them from _config_mod (MetOffice/lfric_core#324). This change has required large-scale matching changes in lfric_atm (MetOffice/lfric_apps/#418). See the following documentation on the config object:

https://metoffice.github.io/lfric_core/how_to_use_it/configuration/using_configuration.html#using-the-config-object