For WRF-Chem Users


If you are a WRF-Chem user but you have found this page through search, congratulations! WRF-GC is a model just like WRF-Chem, but uses chemistry provided by the GEOS-Chem chemical model instead of the chemical schemes in WRF. Learn more about WRF-GC.

This page details some differences (such as advantages) of WRF-GC compared to WRF-Chem. It may be useful to existing WRF-Chem users, because the running workflow of WRF-GC is very similar and you can get up and running quickly.

Major differences to WRF-Chem

  • WRF-GC only supports one chemistry option provided by GEOS-Chem, using chem_opt = 233. WRF-GC must be downloaded separately, replacing the chem folder under WRF. See Downloading WRF-GC.

  • WRF-GC does not use off-line emissions, instead using on-line emissions computed by HEMCO. You do not need to pre-process any emissions data anymore, and can simply configure emissions using a text file. Most inventories, such as CEDS, MIX, NEI, EDGAR, are available out-of-the-box. MEIC emissions for China, etc. are also developed by other groups. WRF-GC is fully compatible with any emission files used by GEOS-Chem users.

WRF-Chem has X feature, does WRF-GC have it?

  • Support for WRF physical/dynamics options… Maybe. But this is also a maybe in WRF-Chem. See Domain, meteorology, and configuration for a table with supported options.

  • Nested domains? Yes.

  • Aerosol-radiation and aerosol-cloud interactions? Yes, using GEOS-Chem aerosols. Feng et al., 2021 GMD describes this capability.

  • Restarts? Yes.

  • Nudging? Yes. See Nudging meteorology.

  • Initial/boundary conditions? Yes, from GEOS-Chem global outputs. See Chemical Initial/Boundary Conditions (IC/BC). We used to support CAM-chem and MOZART4GEOS5 outputs used by WRF-Chem, but this support is deprecated. We recommend running global GEOS-Chem instead. But we use a modified but similar version of mozbc, so you can use CAM-chem/MOZART4GEOS5 outputs at your own risk.

Do I have to run WRF and GEOS-Chem separately?

No, WRF-GC is an online coupled model just like WRF-Chem. Compile them together, run them together.

Does GEOS-Chem output separately?

No, species are written to the wrfout_d0... files like WRF-Chem. Species names are different, and generally are the same as GEOS-Chem.

Can I use offline emissions like WRF-Chem?

No, only HEMCO can be used when GEOS-Chem chemistry is used.

Can I run WRF-GC and WRF-Chem in the same WRF install?

No, they must be installed separately. WRF-GC removes all the existing chemistry in WRF-Chem.

I’m sold! How do I get started quickly, as a WRF-Chem user?

  • You need some GEOS-Chem input files, see Preparing your system. The libraries required for WRF-GC are completely covered by WRF-Chem, so you can reuse the computational environment.

  • You need to replace the chem folder with WRF-GC, see Downloading WRF-GC. Then ./configure -hyb (WRFv3) or ./configure (WRFv4), then you must go to chem and run make install_registry, then go back and ./compile em_real.

  • Everything is configured in namelist.input, set chem_opt=233.

  • No need to prepare emissions input files manually using prep_chem_sources or whatever - HEMCO will do it. Configure emissions using a text file in run/HEMCO_Config.rc.

  • Simply run WRF-GC like before - real.exe, do initial/boundary conditions with our mozbc (Chemical Initial/Boundary Conditions (IC/BC)), then wrf.exe and off you go.