WRF-Chem — Weather Research and Forecasting model with Chemistry
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Overview
========

`WRF-Chem <https://ruc.noaa.gov/wrf/WG11/>`__ is the Weather Research and
Forecasting (WRF) model coupled with chemistry.  It is a fully coupled
online air-quality model, meaning that the meteorological and chemical fields
evolve simultaneously and interact with each other (e.g. aerosol–radiation
feedbacks).

WRF-Chem is a regional limited-area model with nested-domain capability,
making it well suited for high-resolution emission inversion studies at
continental to urban scales.  It supports a wide range of chemical mechanisms
and aerosol modules.

Key features relevant to atmospheric inversion
==============================================

* **Online coupling** — meteorology and chemistry evolve consistently within
  the same time step, avoiding interpolation errors from offline transport.
* **High resolution** — domains can be configured at sub-kilometre resolution.
* **Flexible chemistry** — multiple gas-phase and aerosol mechanisms are
  available (MOZART, RADM2, CBMZ, …).
* **Emission flexibility** — anthropogenic, biogenic, and fire emissions can be
  specified externally.

Key references
==============

* **Grell et al. (2005)** — the original WRF-Chem paper:
  *Fully coupled "online" chemistry within the WRF model*,
  Atmos. Environ., 39, 6957–6975,
  `doi:10.1016/j.atmosenv.2005.04.027 <https://doi.org/10.1016/j.atmosenv.2005.04.027>`__.

* **Skamarock et al. (2021)** — the WRF model description:
  *A Description of the Advanced Research WRF Model Version 4.3*,
  NCAR Technical Note NCAR/TN-556+STR,
  `doi:10.5065/1dfh-6p97 <https://doi.org/10.5065/1dfh-6p97>`__.

Official resources
==================

* `WRF-Chem official page (NOAA/ESRL) <https://ruc.noaa.gov/wrf/WG11/>`__
* `WRF-Chem user guide and tutorial <https://ruc.noaa.gov/wrf/WG11/Users_guide.pdf>`__
* `WRF source code repository (GitHub) <https://github.com/wrf-model/WRF>`__
* `WRF user support forum <https://forum.mmm.ucar.edu/>`__

CIF integration
===============

The CIF WRF-Chem plugin is located under
:doc:`pycif.plugins.models.wrfchem </documentation/plugins/models/wrfchem>`.

.. note::

    The WRF-Chem plugin is currently at a preliminary stage of integration
    into CIF.  Some features (e.g. inline flux optimisation, ensemble member
    handling) require pre-processing outside CIF.  The plugin has been
    developed and tested at DLR (Germany) in the context of regional
    CO₂ inversion studies.

    Preprocessing of WRF input files (``wrfinput``, ``wrfbdy``,
    ``wrfchemi``) is expected to be handled externally before CIF launches
    the model.