Tuning B_1850_C5_CN with different ocean model

[piergiuseppe_fogli@cmcc_it]

I'm running a B_1850_C5_CN compset from cesm_1.1.2 with a different ocean model (i.e. not pop2).
The initial conditions are:
* ocean: blend of WOA 2009 and PHC 3.0.
* CICE: start from scratch
* CLM: created following the User's Guide ("Spinning up the biogeochemistry Carbon-Nitrogen Model (CN spinup)")
* RTM: from the same CLM pinup run.
* CAM: from inputdata/atm/cam/inic/homme/cami_0000-01-01_ne30np4_L30_c120315.nc

After few hundred years of simulation the model is approaching an equilibrium, but the resulting climate is a bit to cold.
From preliminary analysis of the simulation it seems that the cooling is stronger at high latitudes (both hemispheres, especially over North Atlantic/North Seas), where too much sea ice forms. We notice also that the low clouds amount seems overestimated over these regions.
We are trying to increase slightly the CAM namelist variable cldfrc_rhminl, which is warming a bit the simulation, but we have no previous experience with tuning CESM.

Is there any guide for tuning CESM ?
What are the parameters usually used for tuning?
Is there any rationale about how to change these parameters (e.g. is cldfrc_rhminl the right one? does it require to change related parameters?) ?

Any advice would be really appreciated.

Best regards,
Giuseppe Fogli

 

[hannay]

It depends how much imbalance at the TOA you have. If it is not too big, increasing cldfrc_rhminl is a good bet. This will reduce the low cloud globally and it will reduces the cooling at the TOA. 
In some situation, rhminl won't be enough.
THere are other parameters but they will have uneven impact on the globe.How much is your TOA imbalance ? 

 

[piergiuseppe_fogli@cmcc_it]

 RESTOM=FSNT-FLNT= +0.16 W/m2

 

[hannay]

Hi Pier,I was assuming you had a negative TOA imbalance, in which case increasing cldfrc_rhminl would have reduced the low cloud globally and the imbalance at the TOA. Your TOA imbalance is positive. If we decrease the low cloud, it will increase even more. 
If your TOA is positive and the climate is cooling, it is likely the heat is going into the deep ocean.
QUestion about the RESTOM: is it a climatological value averaged over several years (say 20 years) around teh year of your run.
Would it be possible that you plot a timeseries of global annual means for TS and RESTOM (and maybe of the mean ocean temperature)Cecile