Using custom regions with the IMI

The IMI supports regions within the following domains:

  • Africa: 37°S-40°N, 20°W-53°E

  • Asia: 11°S-55°N, 60°E-150°E

  • Europe: (33°N-61°N, 30°W-70°E

  • Middle East: 12°N-44°N, 20°W-70°E

  • North America: 10°N-70°N, 140°W-40°W

  • Oceania 50°S-5°N, 110°E-180°E

  • Russia 41°N-83°N, 19°E-180°E

  • South America 59°S-16°N, 88°W-31°W

These are the nested-grid windows used in GEOS-Chem for which pre-cut meteorological files are available. You may apply the IMI to other regions, but this requires either using global meteorological fields which can be computationally expensive (not recommended) or cropping global meteorological fields via a pre-processing step.

To facilite cropping global meteorological fields, a sample script (crop_met.sh) has been included with the IMI. This script utilizes the Climate Data Operators (CDO) . It also includes an option to first download global meteorological fields at 0.25° x 0.3125° resolution. The global files are large (approx. 300G per month), so when using that option it is recommend that you process short periods at a time and delete the global files before processing additional periods.

In a text editor, modify the user settings section in crop_met.sh. The region defined in crop_met.sh should be the same or larger than the domain defined for your IMI in config.yml.

NestedRegion

Two-letter string to identify region (e.g. SA for South America). This should match the value of NestedRegion in config.yml.

LonMin

Minimum longitude edge of the region of interest.

LonMax

Maximum longitude edge of the region of interest.

LatMin

Minimum latitude edge of the region of interest.

LatMax

Maximum latitude edge of the region of interest.

DownloadGlobalMet

Boolean for downloading global 0.25° x 0.3125° meteorology fields for cropping. Default is true. Set to false if you already have these files on your system.

RemoveGlobalMet

Boolean for deleting global meteorology files after cropping. Default is false. Set to true once you are sure the cropped meteorology files are working properly in the IMI and you do not plan to generate cropped files for additional regions.

InDir

Directory containing the global high-resolution meteorology fields.

OutDir

Directory where the cropped meteorology files will be placed. We recommend specifying this as [YOUR_DATA_PATH]/GEOS_0.25x0.3125_${NestedRegion}/GEOS_FP. Where you replace [YOUR_DATA_PATH] with the same path specified for DataPath in the IMI’s config.yml.

The cropped meteorology files can be generated by then executing ./crop_met.sh at the command line or submitting the script to your cluster’s scheduler if available. Headers for the SLURM scheduler are included at the top of the script, but you can modify or remove those as needed.

To utilize the cropped meteorology files in the IMI, you will need to create a new IMI directory. Modify config.yml so that NestedRegion matches the value set in crop_met.sh. This will automatically add the region ID string in the appropriate locations in the HEMCO_Config.rc files utilized by GEOS-Chem.

If you have regional emissions that you would like to use, please see modifying prior emission estimates.

Finally, you can run the IMI preview to quickly check that the IMI is working as expected for your custom region.