May 2026 – Monthly summary for FESOM2 development Key focus: improve model reliability and accuracy of remapping, diagnostics handling, and solver stability. Delivered features with clear business value and robust cross-grid workflows. 1) Key features delivered: - FESOM Regridding Feature: Implemented unstructured-to-regular grid remapping via the XIOS library, with control-volume bounds for nodes/elements and dateline-aware coordinate handling. Added a sorting subroutine to improve corner coordinate accuracy during remapping. Commit highlights: 9cbbc8a6834d643b73b6f2b8ef1e103c1355864f. 2) Major bugs fixed: - SSH Solver CG Stability and Cleanup: Fixed incorrect allocation for alpha_evp_array in MOD_ICE; added a CG breakdown guard to prevent NaN/Inf propagation; removed verbose CG breakdown debug output. Commits: 2fc3e4fb33a5ccf89a83ef0af04b7fe9a903c512; 4eb2f21dd2bb6bdaa917d75f0175ffd9799a0b6e. - 0D Diagnostics Accumulation and Reset Handling: Ensured 0D CMIP diagnostic fields are accumulated, reset, and averaged before XIOS output; decoupled monthly reset behavior from field naming configuration. Commits: 969c5890e65c81cd647342ed788f721810963652; ed07c0219e04686ea686e6fea34367ba950eed37. 3) Overall impact and accomplishments: - Increased reliability and accuracy of grid remapping and diagnostics, reducing the risk of output mismatches and numerical instability. - Improved data integrity for diagnostic fields and solver operations, contributing to more trustworthy climate projections and better user trust in model outputs. 4) Technologies/skills demonstrated: - Proficiency with XIOS-based remapping workflows and handling of geospatial edge cases (dateline wrap, corner coordinates). - Fortran memory management and array handling to fix stability/robustness bugs in MOD_ICE. - Diagnostic data pipeline improvements and output synchronization prior to XIOS integration. - Debugging discipline to eliminate verbose output without sacrificing traceability. Business value: These changes collectively improve end-user confidence in model outputs, reduce maintenance risk, and lay groundwork for more scalable remapping and diagnostics pipelines.

October 2025 monthly summary focused on correctness and reliability of the ocean model in FESOM/fesom2. Delivered a critical bug fix to metric_factor computation by setting metric_factor to zero per element in oce_mesh.F90, removing the previous tan(ay)/r_earth-based calculation and implementing the change per Qiang's suggestion. This correction improves simulation accuracy and stability, reducing risk of erroneous metric_factor values affecting results. The change is localized to oce_mesh.F90 and is ready for integration with the existing test suite and review. Overall impact: more reliable monthly runs, faster iteration cycles, and clearer guidance for users relying on metric_factor in model setup.

July 2025 (2025-07): Focused delivery of CO2 data outputs readiness in esm_tools. Implemented CO2 Output Enablement by updating XML template to allow CO2 mass mixing ratio and CO2 fluxes to be included in outputs. This work provides the foundation for enhanced CO2 analytics, model validation, and regulatory reporting, enabling more complete environmental data capture across pipelines.