Surface temperature can't be below to 271.4 K in aquaplanet without sea-ice

[jyBear]

I am running som-aquaplanet, without sea-ice in cesm1.2.2. I find that the surface temperature is never below 271.4 K, Even if I change the melt(freezing point). I wonder how the model fix the min surface temperature, and can I change the min surface temperature in aquaplanet?

 

[brianpm]

In CESM1 (and older), the slab-ocean model does not allow the temperature to go below the freezing point of seawater. This is because it expected to make sea ice. When the aquaplanet is configured with the slab-ocean following some very old instructions that I wrote, the sea-ice is turned off because the sea ice model could not run on the atmosphere grid (which the SOM uses).

The temperature is reset as part of the SOM code in cesm1_2_2/models/ocn/docn/docn_comp_mod.F90. Here is the line of code that does it:

o2x%rAttr(kt,n) = max(TkFrzSw,o2x%rAttr(kt,n)) ! reset temp

This behavior is changed in CESM2, in which the SOM aquaplanet can be run using the QSC5 or QSC6 compset.

If there's a reason that you need to run CESM1, you could comment out that line, which should allow the temperature to go below freezing. In CESM2's version of the code, we removed that line for the aquaplanet case (assuming sea ice is NOT running).

 

[jyBear]

Thanks for your reply， I`ll try to change this code.