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E3SM-Project / E3SM

Energy Exascale Earth System Model source code. NOTE: use "maint" branches for your work. Head of master is not validated.
https://docs.e3sm.org/E3SM
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negative litter fluxes to soil #2538

Closed jinyuntang closed 5 years ago

jinyuntang commented 6 years ago

In some configurations (e.g., C-only) of the land bgc model, litter fluxes to soil are found occasionally to be negative. This is due to the lack of explicit constraint on the transfer fluxes between various litter pools in current code. When this is combined with machine roundoff error, given enough time of model integration, some vegetation pools become negative and then iterate with soil bgc pools and fluxes to amplify the negativity. The current code has some fix in the soil bgc pools to suppress the this positive feedback of negativity, but the root cause associated with litter flux is not addressed. This fix will address the root cause of this bug.

jinyuntang commented 6 years ago

a fix is under testing.

thorntonpe commented 6 years ago

@jinyuntang , does this impact all variants of the land BGC code?

jinyuntang commented 6 years ago

@thorntonpe , theoretically, it is. Because the part needs change are shared to among CTC and ECA code. This seems to be the root cause why CNPrecision is needed.

jinyuntang commented 5 years ago

@rljacob, am I unleashed to work on this?

rljacob commented 5 years ago

I just like to make sure every issue has an assignee.

Is this being fixed by PR #2590? Is this issue a duplicate of #2583 ?

jinyuntang commented 5 years ago

@rljacob NO. The negative litter flux issue is a design level bug, and needs to add several subroutines to fix. I have that fixed in my branch, but if OK, I can migrate the fix to a branch derived from the most recent master.

rljacob commented 5 years ago

Ok. The priority should be set by the BGC group leads since this is a BGC function. @kvcalvin or @susburrows

kvcalvin commented 5 years ago

@jinyuntang: I'll need more information on level of effort and how likely the error is to occur before deciding priority. Let's focus on the v1 simulations now and revisit this in January.

Also tagging @bpbond so he is aware.

susburrows commented 5 years ago

@jinyuntang : can you clarify if this bug impacts the configurations used in the v1 CBGC simulations (which include N, P limitation)? Am I understanding correctly that the bug theoretically can impact those simulations, but in practice only rarely causes issues in configurations that include (N,P) nutrient limitations?

jinyun1tang commented 5 years ago

@susburrows , according to @kvcalvin , I will present the results of my exploration next CBGC call. In short, I found it marginally affects CTC, and moderately affect ECA because of some unique feature differences in the vegetation dynamics. From there, we can make a decision on how to proceed in the short and long term.

susburrows commented 5 years ago

OK, thanks for the update!