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AMIP (SST & Sea Ice) Forcing Specifications

The AMIP (Atmospheric Model Intercomparison Project) forcing pipeline ingests observed sea surface temperature (SST) and sea-ice concentration fields from PCMDI to generate monthly boundary condition ancillary files (.anc) for prescribed-ocean experiments in ACCESS-ESM1.6.

Physical Domain & Scientific Scope

  • Boundary Variables Generated:
  • Sea Surface Temperature (sst): Monthly mean sea surface skin temperature. Target STASH item: m01s00i024 (SURFACE TEMPERATURE AFTER TIMESTEP).
  • Sea Ice Concentration (seaice): Fractional area of grid cell covered by sea ice. Target STASH items: m01s00i031 / m01s00i032 (SEA ICE FRACTION).
  • Source Dataset: PCMDI AMIP observational boundary dataset (PCMDI-AMIP-1-1-10, v20250807) spanning 1870 to 2022.
  • UKESM Intermediate Processing: Utilizes the UK Met Office AMIP toolchain (ancillary-file-science on branch 1-port-cmip7-amip-code-for-esm16-site-nci) to regrid PCMDI observations to the N96 atmospheric grid while applying area-preserving Taylor regridding and land-sea mask consistency adjustments.
  • Preservation of Ocean Cells: Unlike land ancillaries which fill missing values with 0.0, AMIP ancillaries maintain strict ocean masks (fill=False in fix_cmip7_ukesm) to avoid corrupting coastal marine boundary temperatures.

Controlling Suite Switches

The execution, experiment inclusion, and script branches for the AMIP pipeline are controlled by parameters in rose-suite.conf:

  • Master Activation Switch: ANCIL_CREATE_AMIP = true
    When set to false, all AMIP regridding and ancillary generation tasks are excluded from the Cylc task graph.
  • Experiment Activation: Governed by USE_EXP['AM'] = True.
  • Variables Processed: AMIP_VARS = ['seaice', 'sst'].
  • Upstream Scripts Branching: Clones the AMIP regridding toolchain from ${GIT_ORG_URL}/${GIT_AMIP_SCRIPTS_REPO}.git on branch ${GIT_AMIP_SCRIPTS_BRANCH} (1-port-cmip7-amip-code-for-esm16-site-nci).
  • Reference: See Suite Configuration & Parameters Reference for full object declarations.

1. AMIP Infrastructure Tasks

git_clone_amip_scripts

  • 1. Description & Purpose: Clones the AMIP processing repository from GitHub (${GIT_ORG_URL}/${GIT_AMIP_SCRIPTS_REPO} on branch ${GIT_AMIP_SCRIPTS_BRANCH}) into ${CYLC_WORKFLOW_SHARE_DIR}/${GIT_AMIP_SCRIPTS_REPO}-amip.
  • 2. Execution: git clone --depth 1 -b ${GIT_AMIP_SCRIPTS_BRANCH} ${GIT_ORG_URL}/${GIT_AMIP_SCRIPTS_REPO}.git.
  • 7 & 8. Output: Cloned directory in workflow share directory.

install_amip

  • 1. Description & Purpose: Installs the cloned AMIP scripts and Python dependencies into the suite's environment.
  • 2. Execution: pip install --no-deps -e ${CYLC_WORKFLOW_SHARE_DIR}/${GIT_AMIP_SCRIPTS_REPO}-amip.

2. Upstream UKESM Regridding Tasks

AM_ukesm_regrid

  • 1. Description & Purpose: Regrids raw monthly PCMDI SST and sea ice NetCDF files to the target N96 resolution using conservative interpolation.
  • 3. Input4MIPs Version: ${CMIP7_AMIP_VERSION} (PCMDI-AMIP-1-1-10), ${CMIP7_AMIP_VDATE} (v20250807), Range: ${CMIP7_AMIP_DATE_RANGE} (187001-202212).
  • 4. Input4MIPs Path: ${VAR.CMIP7_SOURCE_PATH}/AMIP/PCMDI/${CMIP7_AMIP_VERSION}/ocean/mon/{var}/gn/${CMIP7_AMIP_VDATE}/
    (Evaluated: /g/data/qv56/replicas/input4MIPs/CMIP7/AMIP/PCMDI/PCMDI-AMIP-1-1-10/ocean/mon/{var}/gn/v20250807/)

AM_ukesm_taylor

  • 1. Description & Purpose: Applies Taylor diagram verification and conservative flux-conserving smoothing to the regridded SST and sea-ice fields.

AM_ukesm_ancil

  • 1. Description & Purpose: Packages the regridded fields into standardized UKESM intermediate NetCDF files: ${UKESM_AMIP_NETCDF_FILENAME['seaice']} (seaice_amip_n96_gregorian.nc) and ${UKESM_AMIP_NETCDF_FILENAME['sst']} (sst_amip_n96_gregorian.nc).

3. UM Binary Ancillary Generation Tasks

AM_seaice_ancil_amip

  • 1. Description & Purpose: Reads the intermediate ${UKESM_AMIP_NETCDF_FILENAME['seaice']} file, aligns coordinate definitions with the ACCESS-ESM1.6 N96 grid mask without zero-filling ocean points, and produces ${ESM_AMIP_SAVE_FILENAME['seaice']} (seaice_amip_n96_gregorian.anc).
  • 2. CLI Arguments Passed: 
    python -m esm1p6_ancil.amip.cmip7_AM_amip_generate \
    --ancil-target-dirname "${VAR.ANCIL_TARGET_PATH}" \
    # Current: "/g/data/${PROJECT}/${USER}/CMIP7/esm1p6_ancil/$(isodatetime -f CCYY.MM.DD)"
    --cmip7-source-data-dirname "${VAR.CMIP7_SOURCE_PATH}" \
    # Current: "/g/data/qv56/replicas/input4MIPs/CMIP7"
    --esm15-inputs-dirname "${VAR.ESM15_INPUTS_PATH}" \
    # Current: "/g/data/vk83/configurations/inputs/access-esm1p5"
    --esm-grid-rel-dirname "${ESM_GRID_DIRNAME}" \
    # Current: "global.N96"
    --esm15-grid-version "${ESM15_GRID_VERSION}" \
    # Current: "2020.05.19"
    --ukesm-ancil-dirpath "${CYLC_WORKFLOW_SHARE_DIR}/" \
    --ukesm-netcdf-filename "${UKESM_AMIP_NETCDF_FILENAME['seaice']}" \
    # Current: "seaice_amip_n96_gregorian.nc"
    --save-filename "${ESM_AMIP_SAVE_FILENAME['seaice']}"
    # Current: "seaice_amip_n96_gregorian.anc"
  • 5. Scripts & Functions: esm1p6_ancil.amip.cmip7_AM_amip_generate, load_cmip7_ukesm, fix_cmip7_ukesm, save_cmip7_am_amip, save_ancil.
  • 6. Cube Transformations:
    • Loads 3D sea-ice cube (time, lat, lon) spanning 1870–2022.
    • Adjusts latitude and longitude coordinate metadata via fix_cmip7_ukesm(args, ukesm_cube, fill=False).
    • Passes cube to save_ancil with gregorian=False to preserve standard 360-day or Proleptic Gregorian time headers.
  • 7. Produced Ancillary: ${ESM_AMIP_SAVE_FILENAME['seaice']} (seaice_amip_n96_gregorian.anc, 1836 monthly slices, 1870–2022).
  • 8. Destination Path: ${VAR.ANCIL_TARGET_PATH}/modern/amip/atmosphere/boundary_conditions/${ESM_GRID_DIRNAME}/<DATE>/${ESM_AMIP_SAVE_FILENAME['seaice']}.
  • 9. Namelist Updates: None (Generates binary ancillary .anc file).

AM_sst_ancil_amip

  • 1. Description & Purpose: Reads ${UKESM_AMIP_NETCDF_FILENAME['sst']}, validates SST Kelvin units, aligns coordinates without zero-filling ocean cells, and produces ${ESM_AMIP_SAVE_FILENAME['sst']} (sst_amip_n96_gregorian.anc).
  • 2. CLI Arguments Passed: 
    python -m esm1p6_ancil.amip.cmip7_AM_amip_generate \
    --ancil-target-dirname "${VAR.ANCIL_TARGET_PATH}" \
    # Current: "/g/data/${PROJECT}/${USER}/CMIP7/esm1p6_ancil/$(isodatetime -f CCYY.MM.DD)"
    --cmip7-source-data-dirname "${VAR.CMIP7_SOURCE_PATH}" \
    # Current: "/g/data/qv56/replicas/input4MIPs/CMIP7"
    --esm15-inputs-dirname "${VAR.ESM15_INPUTS_PATH}" \
    # Current: "/g/data/vk83/configurations/inputs/access-esm1p5"
    --esm-grid-rel-dirname "${ESM_GRID_DIRNAME}" \
    # Current: "global.N96"
    --esm15-grid-version "${ESM15_GRID_VERSION}" \
    # Current: "2020.05.19"
    --ukesm-ancil-dirpath "${CYLC_WORKFLOW_SHARE_DIR}/" \
    --ukesm-netcdf-filename "${UKESM_AMIP_NETCDF_FILENAME['sst']}" \
    # Current: "sst_amip_n96_gregorian.nc"
    --save-filename "${ESM_AMIP_SAVE_FILENAME['sst']}"
    # Current: "sst_amip_n96_gregorian.anc"
  • 7. Produced Ancillary: ${ESM_AMIP_SAVE_FILENAME['sst']} (sst_amip_n96_gregorian.anc, 1836 monthly slices, 1870–2022).
  • 8. Destination Path: ${VAR.ANCIL_TARGET_PATH}/modern/amip/atmosphere/boundary_conditions/${ESM_GRID_DIRNAME}/<DATE>/${ESM_AMIP_SAVE_FILENAME['sst']}.
  • 9. Namelist Updates: None (Generates binary ancillary .anc file).