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What's New

v2026.09.01 - 10th September 2026

New Features

  • Added extract_meridional_section() method to NEMODataTree:

    • Enables users to extract an approximately meridional section at a chosen longitude from a NEMODataTree.
    • Hydrographic section will be located at the constant i-coordinate whose average longitude (following selection between lat_min and lat_max) is closest to the given longitude.

  • Added concat() and merge() methods of NEMODataTree enabling users to merge variables contained in two or moreNEMODataTrees or concatenate variables contained in two or more NEMODataTrees along a new or existing dimension.

  • Added geoplot() method of NEMODataArray enabling users to plot a 2-dimensional horizontal slice of a variable in geographical coordinates using Cartopy.

Refactored

  • Updated divergence() & curl() method of NEMODataArray to utilise NEMODataArray differencing operations.

Bug Fixes

  • Fix bug ininterp_to() when applied to NEMODataArrays in nested NEMO model domains

Deprecated

  • Deprecated NEMODataTree.gradient() method. Users should use NEMODataArray.derivative() to calculate derivatives of scalar and vector variables along a given dimension.

Documentation

  • Refactored User Guide to include separate sections on NEMO fundamentals, data structures and core operations.
  • Added new NEMODataTree & NEMODataArray methods to How To... Guide..
  • Added new pipelines page to document use of NEMO Pipeline for undertaking NEMO Cookbook diagnostics at scale.

Pull Requests

  • 36 refactor improve performance of nemodatatree constructors by @oj-tooth in https://github.com/NOC-MSM/nemo_cookbook/pull/39
  • 37 feature add nemodataarraygeoplot method by @oj-tooth in https://github.com/NOC-MSM/nemo_cookbook/pull/40
  • 38 refactor improve performance of clip grid by @oj-tooth in https://github.com/NOC-MSM/nemo_cookbook/pull/41
  • Fix for #43 - bug in interp_to() by @atb299 in https://github.com/NOC-MSM/nemo_cookbook/pull/44
  • 45 update geoplot method to support customisation by @oj-tooth in https://github.com/NOC-MSM/nemo_cookbook/pull/48
  • 46 add support for 3 dimensional depth coordinates by @oj-tooth in https://github.com/NOC-MSM/nemo_cookbook/pull/49
  • 47 add option to retain ghost points in nested nemodatatrees by @oj-tooth in https://github.com/NOC-MSM/nemo_cookbook/pull/50
  • 51 feature add extract meridional section method by @oj-tooth in https://github.com/NOC-MSM/nemo_cookbook/pull/56
  • 57 feature automated iperio nftype and name discovery during nemodatatree creation by @oj-tooth in https://github.com/NOC-MSM/nemo_cookbook/pull/58
  • 55 refactor replace existing nemodatatree curl and divergence methods by @oj-tooth in https://github.com/NOC-MSM/nemo_cookbook/pull/59
  • 60 feature add merge and concat methods to combine nemodatatrees by @oj-tooth in https://github.com/NOC-MSM/nemo_cookbook/pull/61
  • 53 docs refactor the nemo cookbook user guide by @oj-tooth in https://github.com/NOC-MSM/nemo_cookbook/pull/62

New Contributors

  • @atb299 made their first contribution in https://github.com/NOC-MSM/nemo_cookbook/pull/44

Full Changelog: https://github.com/NOC-MSM/nemo_cookbook/compare/v2026.06.01...v2026.09.01

v2026.06.01 - 23rd June 2026

New Features

  • Added extract_zonal_section() method to NEMODataTree:

    • Enables users to extract an approximately zonal section at a chosen latitude from a NEMODataTree.
    • Hydrographic section will be located at the constant j-coordinate whose average latitude (following selection between lon_min and lon_max) is closest to the given latitude.

  • Added from_xesmf() accessor forNEMODataArray enabling users to import an xESMF-compatible xarray.Dataset to a NEMO model variable.

  • Add reference vertical scale factors e3{t/u/v/w}_0 and water column heights h{t/u/v/w}_0 to NEMODataTree construction.

New Recipes

  • Two additional NEMO Cookbook Recipes:
  • Extracting Zonal Hydrographic Sections - recipe_extract_rapid.ipynb
  • Working with CMORISED NEMO ocean model outputs - recipe_cmip6.ipynb

Breaking Changes

  • extract_section() expected parameters lon, lat renamed to lon_section, lat_section.

Bug Fixes

  • Fix interp_to(), depth_integral() and transform_vertical_grid() to preserve core dimensions when size(time_counter)=1 - @robertsmalcolm
  • Update _check_grid_dims() to handle singleton dims in domain_cfg
  • Update processing.py to improve performance of merging NEMO gridT and icemod datasets - @atb299

Documentation

  • Added required core dimensions for NEMODataTree constructors to User Guide & How To... Guide.
  • Added two new NEMO Cookbook recipes to documentation.

Pull Requests

  • 29 [feature] add from_xesmf method by @oj-tooth in https://github.com/NOC-MSM/nemo_cookbook/pull/30
  • 32 feature add extract zonal section method to nemodatatree by @oj-tooth in https://github.com/NOC-MSM/nemo_cookbook/pull/33
  • 34 feature add cmorised nemodatatree recipe by @oj-tooth in https://github.com/NOC-MSM/nemo_cookbook/pull/35

Full Changelog: https://github.com/NOC-MSM/nemo_cookbook/compare/v2026.04.0b1...v2026.06.01

v2026.04.b1 - 30th April 2026

New Features

  • Introduction of from_icechunk() and from_zarr() constructors for NEMODataTree:

    • Enables users to open a NEMODataTree from an xarray.DataTree stored in a hierarchical Zarr store or Icechunk store where each group contains one NEMO model grid node dataset.
    • Definition of NEMODataTree grid nodes is now validated to ensure expected coordinates, dimensions, land-sea masks and grid cell scale factors are included.

  • Addition of to_xesmf() accessor forNEMODataArray enabling users to export a NEMO model variable to an xESMF-compatible xarray.Dataset.

New Recipes

  • Three additional NEMO Cookbook Recipes:
  • Regridding using xESMF- recipe_xesmf.ipynb
  • Sea Ice Diagnostics - recipe_sea_ice.ipynb
  • Extracting mask boundaries - recipe_extract_mask_boundary.ipynb

Breaking Changes

  • read_mask=True expects t/u/v/fmaksutil 2-dimensional land-sea unique point masks must be included in the input domain_cfg dataset, otherwise use read_mask=False

Bug Fixes

  • Fix .extract_mask_boundary() and extract.py to support nested NEMO model domains where coordinates are not glamb, gphib
  • **Improved performance of NEMODataArray validation and set_like() methods.

Documentation

  • Update How To... guide to include to_xesmf usage to produce xESMF-compatible xarray.Datasets from NEMODataArrays.
  • Added Marimo and Google Colab notebook previews of all existing NEMO Cookbook recipes, including adding badges to table of recipes in docs.

Pull Requests

  • 16 refactor improve performance of nemodataarray methods by @oj-tooth in https://github.com/NOC-MSM/nemo_cookbook/pull/23
  • 19 add marimo notebook support for recipes by @oj-tooth in https://github.com/NOC-MSM/nemo_cookbook/pull/24
  • 17 feature add from icechunk nemodatatree constructor by @oj-tooth in https://github.com/NOC-MSM/nemo_cookbook/pull/25
  • 22 feature add accessor to support xesmf regridding by @oj-tooth in https://github.com/NOC-MSM/nemo_cookbook/pull/26
  • 20 add new nemo cookbook recipes by @oj-tooth in https://github.com/NOC-MSM/nemo_cookbook/pull/27

Full Changelog: https://github.com/NOC-MSM/nemo_cookbook/compare/v2026.03.0b1...v2026.04.0b1

v2026.03.b1 - 30th March 2026

New Features

  • Introduction of NEMODataArray object, including manual and NEMODataTree constructors:

    • NEMODataArray properties to support grid-aware computation (e.g., .mask, .metrics, .grid etc.).

    • NEMODataArray methods:

      • Masking: .apply_mask().
      • Selections: .sel_like().
      • Grid Operators: .diff(), .derivative(), .integral(), .depth_integral().
      • Statistics: .weighted_mean(), .masked_statistic().
      • Interpolation: .interp_to().
      • Grid Transformations:.transform_vertical_grid().

  • Addition of .depth_integral() method to integrate a variable defined on a given NEMO model grid in depth coordinates between two depth limits.

  • Addition of .weighted_mean() method to perform a grid-aware weighted mean of a variable defined on a NEMO model grid.

  • Update to NEMODataTree constructors:

  • NEMODataTree supports NEMO model outputs using the linear free-surface approximation (i.e., time-independent vertical scale factors) via key_linssh=True.

  • Defined Pixi workspace & environments (pixi.toml) to support NEMO Cookbook development.

New Recipes

  • Two additional NEMO Cookbook Recipes:
  • Upper Ocean Heat Content - recipe_heat_content.ipynb
  • Meridional Ocean Heat Transport - recipe_heat_transport.ipynb

Breaking Changes

  • .transform_to() method to linearly interpolate a variable to a neighbouring NEMO grid renamed to interp_to().

  • Using dictionary syntax to access a variable from a NEMODataTree no longer returns a land-sea masked variable. Instead, an unmasked NEMODataArray is returned, which can be subsequently masked using the .masked attribute.

  • Started Deprecation Cycle for legacy NEMODataTree methods & included deprecation warnings for affected methods. These methods will be removed from NEMO Cookbook in v2026.05 later this year.

Bug Fixes

  • Fix .add_geoindex() using xoak.SklearnGeoBallTreeAdapter & added xoak dependency.
  • Fix .extract_section() to improve boundary indexing and add land-sea masks
  • Fix nested test class TestNEMODataTreeUtils() in test_nemodatatree.py
  • Fix potential NameError in create_section_polygon() where section endpoints share same latitude.
  • Fix TypeError (keep_dims=None) in compute_binned_statistic() in stats.py.
  • Fix alignment error in interpolate_grid() utility function.

Documentation

  • Reorganise User Guide to add NEMO Fundamentals section and improve NEMODataArray description.
  • Update contributing guidance in docs to add getting started with Pixi & GitHub.
  • Add .ipynb template and GitHub Issue template for NEMO Cookbook recipes.
  • Update How To... guide to include NEMODataArray usage.

Full Changelog: https://github.com/NOC-MSM/nemo_cookbook/compare/v2026.01.0b1...v2026.03.0b1

v2026.01.b1 - 18th January 2026

New Features

  • Introduction of NEMODataTree object, including .from_paths() and .from_datasets() constructors.
    • NEMODataTree methods to calculate model grid cell properties (e.g., .cell_area()).
    • NEMODataTree methods to perform grid-aware scalar and vector operations (e.g., .gradient(), .integral().
    • NEMODataTree methods to calculate grid-aware masked and binned statistics (e.g., .masked_statistic(), .binned_statistic())
    • NEMODataTree methods to transform model grid coordinates (e.g., .transform_to())

New Recipes

  • NEMO Cookbook Recipes, including
    1. Meridional overturning stream function in an arbitrary tracer coordinates.
    2. Meridional overturning stream function in depth coordinates (z/z*).
    3. Meridional heat & salt transports.
    4. Surface-forced water mass transformation in potential density coordinates.
    5. Volume census in T-S coordinates.
    6. Masked statistics using bounding boxes and polygons.
    7. Extracting volume transports and properties along the Overturning in the Subpolar North Atlantic array.
    8. Vertical coordinate transformations.
    9. Barotropic stream functions.

Full Changelog: https://github.com/NOC-MSM/nemo_cookbook/commits/v2026.01.0b1