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model aborted due to "column cbalance error"

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model aborted due to "column cbalance error"

Hi Land Model Working Group,

Our group is running the released version of CESM1.2 over Cheyenne (cesm1_2_2_1) with compset B1850C5CN in res f19_g16. We have used dynamic pft by specifying "fpftdyn" in user namelist "user_nl_clm".

After a integration of over 340 model years, the simulation aborted with "column cbalance error".

I have checked this "cbalance error" in this forum, and the link below shows that a total of 4 posts with 3 of them having very similar problems of cbalance we are having, but I couldn't find clear answers from any of the posts.

I'm wondering whether the LMWG can give me some hints about how to solve this error. 

Thank you very much for your time!




48: column cbalance error =   1.263106241822243E-008       11319

48: begcb       =    111711217.054611

48: endcb       =    111749016.684045

48: delta store =    37799.6294338852

48: input mass  =   0.000000000000000E+000

48: output mass =   -37799.6294338978

48: net flux    =    37799.6294338978

48: nee         =   -37799.6294338978

48: gpp         =   0.000000000000000E+000

48: er          =   -37799.6294374520

48: col_fire_closs         =   0.000000000000000E+000

48: col_hrv_xsmrpool_to_atm =  -7.925924159820731E-008

48: dwt_closs         =   9.654961837841052E-008


48: product_closs         =   3.536909218513369E-006



There is a crop pft in one gridcell that seems to be causing the problem.  It has very small negative nitrogen pools and fluxes (e.g., for the leaf) that eventually causes some bad behavior in downregulation of gpp and consequently lai as well (an lai value of 12000 eventually) that does appear to eventually crash the model.  So I do think it is likely that it is a land problem after all in this particular case. There are some precision controls on small negative/postive carbon/nitrogen pools that are supposed to help with these types of problems by zeroing out the bad values.  However, the precision control on most of the nitrogen variables is triggered by the corresponding carbon values and in this case the carbon values are not quite small enough to trigger the precision control for nitrogen. The underlying cause of these small negative values is not clear.  What I recommend for now is to increase the nitrogen and carbon precision thresholds as well as the carbon and nitrogen balance check thresholds slightly.  This should nudge the pft into a more normal state.  This is just a slight perturbation to the land state and won't change climate.I've tried this myself by restarting the case at 0344-01 (this is when the carbon value is still small enough to trigger the precision control using the new threshold) and was able to run successfully for five more years.  There is a chance of course the problem could reappear. So, in CNPrecisionControlMod.F90, change the "ncrit" and "ccrit" values to 1.e-7_r8.And in CNBalanceCheckMod.F90, change the carbon and nitrogen balance thresholds to 1.e-7_r8 as well.
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