Testing FATES two-stream radiation scheme is activated by switching the fates_rad_model parameter from 1 to 2. This is all that is needed, both radiation schemes 1) Norman and 2) two-stream use the same optical parameters. fates_rad_model Note that to avoid exceeding the filename string length maximum, the parameter file generated on the fly is placed in the $SRCROOT/src/fates/parameter_files directory. This may still run into problems is the $SRCROOT string is too long. Like the test with seed dispersal activation, the main downside of this method is that this file will require a custom update for every fates parameter file API update. Addressing CTSM issue #2126 will alleviate this issue as it will provide the capability to build the fates parameter file on the fly which with the appropriate values for this test.