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Adding a new forcer to Hector

Source: vignettes/articles/addnewforcer.Rmd
addnewforcer.Rmd

Objective

Here are some notes about how to add a new species that will affect Hector’s radiative forcing budget in order to answer the question “how much impact does this newly discovered forcer X have.”

Here are some notes as to how to do this:

  • Option 1: add the estimated radiative forcing values to the miscellaneous radiative forcing variable
  • Option 2: add a new component to Hector and pass the appropriate information to Hector’s forcing components

Option 1

Use Hector’s miscellaneous radiative forcing variable to read additional radiative forcing values.

This approach requires little to no coding experience but does require that the users have radiative forcing values readily available. Users can read in the new radiative forcing values via the ini file with the Fmisc variable. Fmisc is a column in the Hector csv input tables named something like ssp434_emiss-constraints_rf.csv. Depending on the user configuration, Fmisc may have numeric values or will be equal to all zeros. If Fmisc is non-zero, then the user should add the new values to the existing values. Alternatively, using the Hector R package, users can read in miscellaneous forcing to a Hector core with RF_MISC() and the setvar() function.

Option 2

Add the new forcer to Hector; this will require changes to the C++ code base.

  1. Create a new Hector component: use an existing model component or the dummy_model_component.hpp and dummy_model_component.cpp files as a template.
  2. Within the new component, add new variables as appropriate. Use this component to read in the emissions. If the forcer being added is a GHG, use the appropriate method to convert from emissions to concentrations and expose the concentrations (via getData) so that they may be passed to other Hector components. The new model component cpp file will return the new emissions or concentrations (whichever one is appropriate).
  3. Next, modify the forcing_compoent.cpp. Add the equation that converts the emissions or concentration time series to radiative forcing values. The new values should be added into the forcing map (“forcings”, see where the N2O RF is set for an example) so that these new values will be incorporated into the total radiative forcing calculation.
  4. Lastly, make sure to update the rcpp_constants.cpp so that the new variables can be accessed via the R interface (see new variables).