[RegCNET] Greenhouse gas concentration tweak

[Insel Nadja]

Good afternoon.

I am using RegCM 4.4.5 to simulate paleoclimate conditions over the western US. I have not used this specific version before and I just saw in the user guide that this version includes a tweakparam namelist. If I want to change greenhouse gas concentrations to past values, can I just calculate a tweak factor to get the desired greenhouse gas concentrations without changing the values within the radiation files? For example, if the model runs on modern default conditions, i.e. co2vmr = 3.55e-4 is it possible to just define tweak_greenhouse_gases =1, and a gas_tweak factor of 0.77 to get a concentration of 273ppm? Or do the GG concentrations still need to be modified in mod_rad_radiation?  

Thank you for clarifying.
Nadja