Slab ocean model equilibration times

[pksnyder@umn_edu]

Hello,

I am running the default CAM3 with the SOM configuration. I was curious as to what the expected equilibration times are for the model. I know that the manual specifies "Forty years or more of integration time may be needed for the model to reach a quasi-equilibrium state." Is this equilibration time resolution dependent? I have started a standard control run at T85 and I am having difficulty getting the model to equilibrate (using globally averaged TS and TOA radiative balance as the indicators). As background, I ran the model for 50 years and used the last 25 for creation of the SOM data set. I then started the model at year 50 and have been running for about 75 years. While globally averaged TS seemed to level off at ~287.8K in about 40-50 years, it then began a drop to its current value of ~287.4K and cooling. Does this seem reasonable? Should I expect longer equilibration times because I am running at T85, or is that not important?

Thanks,
Peter

 

[rneale]

You shouldn't expect longer equilibrium times because you are running at higher resolution. 0.4K seems a lot of drift after 40 years though. Did you plot the timeseries of top of atmosphere energy balance in the model. You can get this by calculating global averages of FSNT-FLNT. This should be close to zero for equilibrium. When you calculated the Qfluxes from the fixed SST experiment was the long term budget at the top of atmosphere near zero for the second 25 years you used?