There are two knobs which can be used in the control file for bottom friction. The usual way of specifying bottom friction would be to either use the default value of 'Baro_rayl', or to specify a different value in the control file. This then adds the appropriate explicit term to the baroclinic momentum equations at the bottom grid points adjacent to topography and also as an implicit term in the barotropic stream function equation. If the barotropic component is not used (i.e., is assumed to be zero), then explicit bottom friction can be added by setting 'Bottom_friction' in the control file. If both 'Baro_rayl' and 'Bottom_friction' are set in the control file, then 'Baro_rayl' will be used as the parameter for the implicit term in the barotropic equation, and 'Bottom_friction' will be used as the parameter for the explicit term in the baroclinic momentum equations. The user is responsible for any discrepancies!