[QUESTION] Nested grid simulation negative concentration error

[tessac2]

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Hello, I have been running GEOS-Chem version 13.2.1 nested grid simulation. Before starting the nested grid simulation, I ran at 4x5 resolution for the years 2018-2020. I want to run the nested grid simulation for 2019 over North America at 0.25x0.3125 resolution. I was able to run from June 1 through October 24 at 2 week increments. However, on October 24 the run stops, saying that there is a negative concentration for SO2 and the error was encountered in "D0_Tend" and "Do_Mixing". I tried recompiling and running with the compiler debug flags, following the solution outlined in #712 & #1081 but that did not seem to solve the issue. I was wondering if you had any suggestions on what to try next?

[yantosca]

Thanks for writing @tessac2. One thing you can try is to increase the size of the nested-grid transport buffer zone as described in this issue: https://github.com/geoschem/geos-chem/discussions/875#discussioncomment-1415092.

I think there have also been some fixes added since 13.2.1. Another thing you can do is just to zero out the negative concentrations if they occur.

[yantosca]

@tessac2: I wonder also if SO2 is getting titrated out due to wet deposition or chemistry. You could also try some short simulations turning those operations off to see if you don't get the negatives.

[tessac2]

Thanks Bob! I tried increasing the size of the nested-grid transport buffer zone and got the same error message, so I will try the other solutions you presented next!

[tessac2]

Hi Bob, I was wondering how I would zero out the negative concentrations if they were to occur, or if there is a previous GitHub that directs on how to do this? Similarly for turning off the wet deposition. My worry with that is that there are multiple grid boxes with the negative concentration at different vertical levels

GC.log.20191016_1101.txt

[yantosca]

Hi Tessa. You could comment out the error code and add an IF statement here in mixing_mod:

#else

                IF ( ( N /= id_CH4_SAB ) .and. ( N /= id_CO2 ) ) THEN

                 ! KLUDGE: skip the warning message for CH4_SAB, which can be
                 ! negative (it's a soil absorption flux).  The TagCH4
                 ! simulation is not used regularly as of Feb 2021 -- fix this
                 ! later if need by. (bmy, 2/25/21)
!                 Print*, 'WARNING: Negative concentration for species ',     &
!                          TRIM( SpcInfo%Name), ' at (I,J,L) = ', I, J, L
!                 ErrorMsg = 'Negative species concentations encountered.' // &
!                            ' This may be fixed by increasing the'        // &
!                            ' background concentration or by shortening'  // &
!                            ' the transport time step.'
!                 RC = GC_FAILURE

                  ! Zero out negative values
                  IF ( State_Chm%Species(I,J,L,N) < 0 ) THEN
                      State_Chm%Species(I,J,L,N) = 0.0_fp
                ENDIF
#endif

That should prevent negatives from happening. Let me know if that works.

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[tessac2]

@yantosca Sorry I forgot to follow up--that fix you suggested helped! Thank you!

[tessac2]

@yantosca Hello! I have been able to run GEOS-Chem with the amended mixing_mod to 0 out negative concentrations. However, I am now running into an issue on April 9, 2020 (so almost 6 months after the original issue in October 2019) where there is now an issue with the wetdep. I was wondering if this could be related to the 0s--it seems like the day before the simulation stopped running that there were a lot 0s.

GC.log.20200401_0416.txt

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This issue has been automatically marked as stale because it has not had recent activity. If there are no updates within 7 days it will be closed. You can add the "never stale" tag to prevent the Stale bot from closing this issue.

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Closing due to inactivity