regional-mom6

Python package for automatic generation of regional configurations for the Modular Ocean Model version 6 (MOM6)

Users just need to provide some information about where, when, and how big their domain is and also where raw input forcing files are. The package sorts out all the boring details and creates a set of MOM6-friendly input files along with setup directories ready to go!

The idea behind this package is that it should let the user sidestep some of the tricky issues with getting the model to run in the first place. This removes some of the steep learning curve for people new to working with MOM6. Note that the resultant model configuration might still need some tweaking (e.g., fiddling with timestep to avoid CFL-related numerical stability issues or fiddling with bathymetry to deal with very narrow fjords or channels that may exist).

Features

• Automatic grid generation at chosen vertical and horizontal grid spacing.
• Automatic removal of non-advective cells from the bathymetry that cause the model to crash.
• Handle slicing across 'seams' in of the forcing input datasets (e.g., when the regional configuration includes longitude 180 and the forcing longitude is defined in [-180, 180]).
• Handles metadata encoding.
• Creates directory structure with the configuration files as expected by MOM6.
• Handles interpolation and interpretation of input data. No pre-processing of forcing datasets is required. (In some cases, slicing the forcing dataset before helps with hitting limitations related to the machine's available memory.)

Limitations

• Only generates regional horizontal grids with uniform spacing in longitude and latitude. However, users can provide their own non-uniform grid, or ideally open a pull request with a method that generates other types of horizontal grids.
• Only supports boundary segments that are parallel to either lines of constant longitude or lines of constant latitude.

We want to hear from you

If you have any suggestions please feel free to open an issue or start a discussion. We welcome any new contributors and we are very keen to help you out along the way!

What you need to get started:

1. a cool idea for a new regional MOM6 domain,
2. a working MOM6 executable on a machine of your choice,
3. a bathymetry file that at least covers your domain,
4. 3D ocean forcing files of any resolution on your choice of A, B, or C Arakawa grid,
5. surface forcing files (e.g., from ERA or JRA reanalysis), and
6. GFDL's FRE tools be downloaded and compiled on the machine you are using.

Check out the documentation and browse through the demos.

Installation

We encourage creating a new or using an existing conda environment.

Easy, clean, one liner via conda

The easiest way to install regional-mom6 is via conda.

conda install conda-forge::regional-mom6

That's it -- now enjoy!

"But I want pip, can't I install with pip?"

To install via pip is a bit more cumbersome.

A prerequisite is the binary esmpy dependency, which provides re-gridding capabilities. The easiest way to install esmpy is via conda:

conda install -c conda-forge esmpy

Alternatively, to install esmpy in a Conda-free way, follow the instructions for installing ESMPy from source. With esmpy available, we can then install regional-mom6 via pip. (If we don't have have pip, then conda install pip should do the job.)

With esmpy installed we can now install regional-mom6 via pip:

pip install regional-mom6

The above installs the version of regional-mom6 (plus any required dependencies) that corresponds to the latest tagged release of the package.

"I want to live on the edge! I want the latest developments"

To install regional-mom6 directly from the GitHub repository using pip, first install esmpy as described above. Then:

pip install git+https://github.com/COSIMA/regional-mom6.git

to get the version that corresponds to the latest commit in GitHub. Alternatively, install the version that corresponds to a particular git commit using, for example,

pip install git+https://github.com/COSIMA/regional-mom6.git@061b0ef80c7cbc04de0566df329c4ea472002f7e

MOM6 Configuration and Version Requirements

The package and demos assume a coupled MOM6-SIS2 configuration, but also work for MOM6 ocean-only configuration after appropriate changes in the input.nml and MOM_input files.

Additionally, regional configurations require that the MOM6 executable must be compiled with symmetric memory.

The current release of this package assumes the latest source code of all components needed to run MOM6 as of January 2024. A forked version of the setup-mom6-nci repository contains scripts for compiling MOM6 and, furthermore, its src directory lists the particular commits that were used to compile MOM6 and its submodules for this package.

Note that the commits used for MOM6 submodules (e.g., Flexible Modelling System (FMS), coupler, SIS2) are not necessarily those used by the GFDL's MOM6_examples repository.

Getting started

The example notebooks walk you through how to use the package using two different sets of input datasets. Please ensure that you can get at least one of these working on your setup with your MOM6 executable before trying to modify the example to suit your domain with your bathymetry, forcing, and boundary conditions.

You can download the notebooks from Github or by clicking on the download button, e.g., at the top-right of the regional Tasmania forced by ERA5 example.

Citing

If you use regional-mom6 in research, teaching, or other activities, we would be grateful if you could mention regional-mom6 and cite our paper in JOSS:

Barnes et al., (2024). regional-mom6: A Python package for automatic generation of regional configurations for the Modular Ocean Model 6. Journal of Open Source Software, 9(100), 6857, doi:10.21105/joss.06857.

The bibtex entry for the paper is:

@article{regional-mom6-JOSS,
  doi = {10.21105/joss.06857},
  url = {https://doi.org/10.21105/joss.06857},
  year = {2024},
  publisher = {The Open Journal},
  volume = {9},
  number = {100},
  pages = {6857},
  author = {Ashley J. Barnes and Navid C. Constantinou and Angus H. Gibson and Andrew E. Kiss and Chris Chapman and John Reily and Dhruv Bhagtani and Luwei Yang},
  title = {{regional-mom6: A Python package for automatic generation of regional configurations for the Modular Ocean Model 6}},
  journal = {Journal of Open Source Software}
}