add_reconstruction_weights

utils/omega/add_reconstruction_weights.py is a standalone script that computes edge vector reconstruction weights and appends them to an existing MPAS-Ocean or Omega mesh file.

The weights are computed using the least-squares method described in Peixoto and Barros (2014) using a two-ring edge stencil (see Figure 5 of that paper).

The script auto-detects whether the input file uses MPAS-Ocean or Omega naming conventions and writes output in the same convention. Only the small mesh/grid variables are loaded; large state/tracer fields are skipped, making it safe to run on production meshes.

Usage

./utils/omega/add_reconstruction_weights.py \
    -i <input_mesh.nc> \
    -o <output_mesh.nc> \
    [-w <num_workers>] \
    [-c <chunk_size>]

Flag	Description
-i / --input_file	Input mesh file (MPAS-Ocean or Omega format)
-o / --output_file	Output file (copy of input with weights appended)
-w / --num_workers	Number of dask worker processes (enables parallel mode)
-c / --chunk_size	Cells per dask chunk (default: 1000)

Passing either -w or -c enables dask parallelism. If -c is given without -w, the worker count is inferred from mache (requires running on a recognised machine).

Parallel performance

The script uses a local multiprocessing dask scheduler and can exploit all cores on a single node. Based on timing tests on Chrysalis with the EC30to60 mesh (~1.8 M cells, 32 workers):

num_workers	chunk_size	wall time
32	7000	~5m 57s
32	3700	~4m 42s
32	1850	~4m 16s

Fewer workers with more, smaller chunks per worker tends to be faster than filling each worker with one large chunk. Start with a chunk size that gives several chunks per worker and tune from there.