Perpetual monthly simulations in CESM2 (F2000climo): Fixing solar insolation to a specific month.

[shameela_iisc]

Hello CESM community,

I am trying to set up perpetual monthly simulations in CESM2.1.5 using the F2000climo compset in prescribed SST mode, and I would like to confirm the correct way to keep solar insolation fixed to a particular month.

The aim is to isolate month-specific atmospheric responses (e.g., cloud and energy balance adjustments) by fixing boundary conditions to a single calendar month.
I plan to run 12 control simulations: Perp_Jan, Perp_Feb, …, Perp_Dec each with SST, sea ice, and insolation fixed to that month.

I am currently planning to fix insolation using the following CAM namelist settings:
perpetual = .true.
perpetual_month = 1
where perpetual_month = 1 for January, 2 for February, etc.

Is this the correct and recommended way to impose perpetual monthly insolation in CESM2?

1. Does perpetual_month fully fix the solar declination and zenith angle throughout the integration, even as the model calendar advances?
2. Are there any additional namelist or XML settings required to prevent unintended seasonal progression of insolation?
3. Is there any caveat specific to F2000climo or prescribed SST runs that I should be aware of?

Any guidance or confirmation from users who have implemented similar setups would be greatly appreciated.