OpenGHG Inversions

OpenGHG Inversions is a Python package that is being develoepd as part of the OpenGHG project with the aim of merging the data-processing and simulation modelling capabilities of OpenGHG with the atmospheric Bayesian inverse models developed by the Atmospheric Chemistry Research Group (ACRG) at the University of Bristol, UK.

Currently, OpenGHG Inversions includes the following regional inversion models:

• Hierarchical Bayesian Markov Chain Monte Carlo (HBMCMC) model (as described in Ganesan et al., 2014, ACP)

Installation and Setup

As OpenGHG Inversions is dependent on OpenGHG, please ensure that when running locally you are using Python 3.10 or later on Linux or MacOS. Please see the OpenGHG project for further installation instructions of OpenGHG and setting up an object store.

Setup a virtual environment

Check that you have Python 3.10 or greater:

python --version

(Note for Bristol ACRG group: If you are on Blue Pebble, the default anaconda module lang/python/anaconda is Python 3.9. Use module avail to list other options; lang/python/miniconda/3.10.10.cuda-12 or lang/python/miniconda/3.12.2.inc-perl-5.30.0 will work.)

Make a virtual environment

python -m venv openghg_inv

Next activate the environment

source openghg_inv/bin/activate

Installation using pip

First you'll need to clone the repository

git clone https://github.com/openghg/openghg_inversions.git

Next make sure pip and related install tools are up to date and then install OpenGHG Inversions using the editable install flag (-e)

pip install --upgrade pip setuptools wheel
pip install -e openghg_inversions

Optionally, install the developer requirements (there is more information about this in the "Contributing" section below):

pip install -r requirements-dev.txt

Verify that PyMC is using fast linear algebra libraries

At this point, run

python -c "import pymc"

This should run without printing any messages. If you receive a message about pymc or pytensor using the numpy C-API, then your inversions might run slowly because the fast linear algebra libraries used by numpy haven't been found.

Solutions to this are:

1. try python -m pip install numpy after upgrading pip, setuptools, wheel
2. create a conda env, install numpy using conda, then use pip to upgrade pip, setuptools, wheel and install openghg_inversions

Using OpenGHG Inversions

Getting Started

For an overview of OpenGHG inversions, see this primer.

Passing parameters to the inversion

Keyword arguments are propagated as follows:

1. any key-value pair in an ini file or passed via the --kwargs flag is passed to the MCMC function as a keyword argument. (Currently, fixedbasisMCMC is the only available MCMC function)
2. any keyword argument not recognised by the MCMC function (i.e. fixedbasisMCMC) is passed to the function inferpymc in hbmcmc.inversion_pymc, which is the function that creates and samples from the RHIME model.

Thus you can pass arguments to either fixedbasisMCMC or inferpymc, but all of these arguments will be specified in the ini file (or command line).

Let's look at these two steps in detail.

Ways of passing arguments to the inversion

Passing options in an ini file

Extra options can be added to an ini file in almost any location. The template ini file puts these option under the heading MCMC.OPTIONS:

[MCMC.OPTIONS]
averaging_error = True
min_error = 20.0
fixed_basis_outer_regions = False
use_bc = True
nuts_sampler = "numpyro"
save_trace = True
compute_min_error = True
no_model_error = False

These will be passed to the MCMC function (e.g. fixedbasisMCMC) as keyword arguments. Any argument in fixedbasisMCMC can be specified in an ini file this way.

Passing options at the command line

When running inversions using the script run_hbmcmc.py, you must specify the start and end date of the inversion period, and you pass an ini file using the flag -c.

In addition, you can pass the output path using the flag --output-path; this is useful if your SLURM script uses different output locations for different array jobs.

You can also pass arbitrary keyword arguments to run_hbmcmc.py using the --kwargs flag. For instance:

python run_hbmcmc.py "2019-01-01" "2019-02-01" -c "example.ini" --kwargs '{"averaging_error": true, "min_error": 20.0, "nuts_sampler": "numpyro"}'

It is crucial that you enclose the dictionary in single quotes, otherwise the command line will split the dictionary on white space.

Again, this can be used to change the arguments passed to an inversion on the fly (say, in a SLURM script).

The format of the dictionary inside single quotes must be JSON, because the value of kwargs is parsed using json.loads. Python translates JSON according to this table. In particular, "true" in JSON translate to True in Python (but "True" will be translated as a string).

The parsing in our ini files is more flexible; in particular, values that are Python statements will be translated to Python, so you don't need to worry about translation.

What parameters can you set?

The following sections detail some parameters that enable/specify optional behaviour in the inversion.

Parameters for fixedbasisMCMC

This is not a comprehensive list (see the docstring for fixedbasisMCMC in the hbmcmc module for more arguments).

• save_trace:
  • The default value is False.
  • If True, the arviz InferenceData output from sampling will be saved to the output path of the inversion, with a file name of the form f"{outputname}{start_data}_trace.nc. To load this trace into arviz, you need to use InferenceData.from_netcdf.
  • Alternatively, you can pass a path (including filename), and that path will be used.
• averaging_error: if True, the error from resampling to the given averaging_period will be added to the observation's error.
• use_bc: defaults to True. If False, no boundary conditions will be used in the inversion. This implicitly assumes that contributions from the boundary have been subtracted from the observations.
• fix_basis_outer_regions:
  • Default value is False
  • If True, the "outer regions" of the (EUROPE) domain use basis regions specified by a file provided by the Met Office (from their "InTem" model), and the "inner region", which includes the UK, is fit using our basis algorithms.
  • This option is only available for the EUROPE domain currently.
• calculate_min_error: calculate min_error (see below) on the fly using the "residual error method"
• filters: filters to apply to data (after it is resampled and aligned)
  • filters = None will skip filtering
  • if filters is a list of filters (or a string containing a single filter name), those filters will be applied to all sites.
  • if filters is a dictionary with site codes as keys and lists of filters as values, then each site will have filters applied individually according to this dictionary. All sites must supplied; to skip a site, pass None instead of a list. For instance: filters = {"MHD": ["pblh_inlet_diff", "pblh_min"], "JFJ": None}.
  • the list of available filters can be found in the filtering function in the utils module.

Parameters for inferpymc

As mentioned above, any keyword argument passed to fixedbasisMCMC (either by an ini file or from --kwargs on the command line) that is not recognised by fixedbasisMCMC is passed on to inferpymc.

These parameters include:

• min_error: a non-negative float value specifying a lower bound for the model-measurement mismatch error (i.e. the error on (y - y_mod)).
• nuts_sampler: a string, which defaults to "pymc". The other option is "numpyro", which will the JAX accelerated sampler from Numpyro; this tends to be significantly faster than the NUTS sampler built into PyMC.
• pollution_events_from_obs: Determines whether the model error is calculated as a fraction of:
  • the measured enhancement above the modelled baseline (if True)
  • the prior modelled enhancement (if False)
• no_model_error: if True, only use obs error in likelihood (omitting min. model error and model error from scaling pollution events).

The output from inversions

The results of an inversions are returned as an xarray Dataset.

The dimension nmeasure consists of the time for each observation stacked into a single 1D array.

TODO: complete this part

• Yerror: obs. error used in the inversion; if add_averaging is True, this will contain the combined "repeatability" and "variability"; otherwise, it will just contain "repeatability", if it is available, or "variability"
• Yerror_repeatablity: obs. repeatability. If repeatability isn't available for some sites, then this is filled with zeros.
• Yerror_variability: obs. variability.

Contributing

To contribute to openghg_inversions, you should also install the developer packages:

pip install -r requirements-dev.txt

This will install the packages flake8, pytest, black.

We use black to format our code. To check if your code needs reformatting, run:

black --check openghg_inversions

in your openghg_inversions repository (with your virtual env activated). If you replace the flag --check with --diff, you can see what will be changed.

To make these changes, run

black openghg_inversions

We also recommend using flake8 to check for code style issues, which you can run with:

flake8 openghg_inversions

You can run the tests using:

pytest

in the openghg_inversions repository. (Make sure your virtual env is activated.)

To contribute new code, make a branch off of the devel branch. When your code is ready to be added, push it to github (origin). You can then open a "pull request" on github and request a code review. It's helpful to write a description of the changes made in your PR, as well as linking to any relevant issues.

Your code must past the tests and be reviewed before it can be merged. After this, you can merge your branch and close it (it can always be recovered later if necessary).

References

Ganesan et al. (2014),ACP;

Western et al. (2021), Enviro. Sci. Tech Lett.