Remapping

This page focuses on how remapping works in i7aof and what you can configure. It complements the end‑to‑end End‑to‑End Workflows page without repeating it.

What is remapped and when

  • CMIP CT/SA after TEOS‑10 conversion (per scenario): ismip7-antarctic-remap-cmip

  • Climatology CT/SA (once): ismip7-antarctic-remap-clim

Both paths prepare the vertical coordinate to a dense z_extrap before the horizontal remap to the ISMIP grid.

ISMIP grid definitions

Grid descriptions, coordinates, and bounds are provided by i7aof.grid.ismip. The target grid is specified in your config, and filenames include an ismip<res> tag (e.g., ismip8km).

Methods and when to use them

The remap method is selected via [remap] method in your config and may differ by variable:

  • Bilinear: good default for smoothly varying ct and sa.

  • Conservative: use when integral preservation across cell areas matters.

  • Nearest‑stod: fallback for categorical masks or extremely sparse regions.

Mask handling: invalid cells are masked prior to interpolation; a valid‑fraction normalization is applied during the vertical stage to minimize edge artifacts.

Vertical preparation (to z_extrap)

  • Convert the model/climatology vertical coordinate to a monotonic height axis.

  • Interpolate to dense z_extrap levels to support robust extrapolation later.

  • Enforce dimension order (z_extrap, y, x) for consistency.

Configuration keys

[remap_cmip]
vert_time_chunk = 1
horiz_time_chunk = 120
method = bilinear        # or conservative, nearest

[remap_clim]
method = bilinear

Tune horiz_time_chunk to balance memory and throughput; keep vert_time_chunk = 1 unless vertical processing becomes dominant.

Note: For now, it is not recommended that you change the remapping method, since we have only tested bilinear and there is reason to think that the other methods would lead to unphysically blocky results.

Outputs

<workdir>/remap/<source>/<tag>/.../*_{ct,sa}_remap.nc           # CMIP
<workdir>/remap/climatology/<clim>/*_ismip<res>.nc              # Climatology

Validation checklist

  • Coordinates carry ISMIP grid bounds; CF attributes preserved.

  • No large holes introduced near complex coastlines (inspect masks).

  • Values are within physical ranges; spot‑check against native grid statistics.

Tips

  • Use bilinear for speed unless conservation is essential.

  • If performance is I/O‑bound, increase horiz_time_chunk; if memory spikes, reduce it.

See also: Climatology Workflows for recommended climatology choices and CMIP Model Inputs for CMIP input preparation.