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Known issues in CESM2.0 CAM-chem compsets

mmills

mmills

CSEG and Liaisons
Staff member
Affected Releases CESM2.0.0Errors have been found in 3 surface emissions files used in WACCM and CAM-chem compsets with tropospheric chemistry (TS1 or TSMLT1). The affected compset are:CAM-chem TS1 Compset Alias: Compset Long name   FC2000climo     : 2000_CAM60%CCTS_CLM50%BGC-CROP_CICE%PRES_DOCN%DOM_MOSART_CISM2%NOEVOLVE_SWAV   FC2010climo     : 2010_CAM60%CCTS_CLM50%BGC-CROP_CICE%PRES_DOCN%DOM_MOSART_CISM2%NOEVOLVE_SWAV   FCHIST             : HIST_CAM60%CCTS_CLM50%BGC-CROP_CICE%PRES_DOCN%DOM_MOSART_CISM2%NOEVOLVE_SWAV   FCSD                 : SDYN_CAM60%CCTS_CLM50%BGC-CROP_CICE%PRES_DOCN%DOM_MOSART_SGLC_SWAVWACCM TSMLT1 Compset Alias: Compset Long name   BW1850            : 1850_CAM60%WCTS_CLM50%BGC-CROP_CICE_POP2%ECO_MOSART_CISM2%NOEVOLVE_WW3   FWHIST            : HIST_CAM60%WCTS_CLM50%BGC-CROP_CICE%PRES_DOCN%DOM_MOSART_CISM2%NOEVOLVE_SWAV   FW1850             : 1850_CAM60%WCTS_CLM50%BGC-CROP_CICE%PRES_DOCN%DOM_MOSART_CISM2%NOEVOLVE_SWAV   FW2000             : 2000_CAM60%WCTS_CLM50%BGC-CROP_CICE%PRES_DOCN%DOM_MOSART_CISM2%NOEVOLVE_SWAV   FWSD                : SDYN_CAM60%WCTS_CLM50%BGC-CROP_CICE%PRES_DOCN%DOM_MOSART_SGLC_SWAVUsers should use corrected emissions in these compsets with the following steps:1. Create a case, and run case.setup and preview_namelists in the case directory in order to create the atmosphere namelist file atm_in in the CaseDocs subdirectory.2. Copy the entire "srf_emis_specifier" list from CaseDocs/atm_in into the user_nl_cam file3. Edit the user_nl_cam specification to replace the 3 files:a. Replace emissions-cmip6_BIGALK_bb_surface_1750-2015_0.9x1.25_c20170322.nc with emissions-cmip6_BIGALK_bb_surface_1750-2015_0.9x1.25_c20180611.ncb. Replace emissions-cmip6_BIGENE_bb_surface_1750-2015_0.9x1.25_c20170322.nc with emissions-cmip6_BIGENE_bb_surface_1750-2015_0.9x1.25_c20180611.ncc. Replace emissions-cmip6_NO_bb_surface_1750-2015_0.9x1.25_c20170322.nc with emissions-cmip6_NO_bb_surface_1750-2015_0.9x1.25_c20180611.ncThese corrected emissions files have been added to the inputdata repository, and CESM will automatically retrieve them.
 
mmills

mmills

CSEG and Liaisons
Staff member
Affected Releases CESM2.0.0A bug has been found in the release code of CESM2.0.0 regarding the evaporation of rain number in Morrison-Gettelman V2 (MG2) cloud microphysics. This bug has been fixed in the cam6_0_005 tag, which was checked in to the CAM development trunk on July 16, 2018. Testing in a coupled piControl simulation reveals the effects of fixing this bug to be very small in the global average. A global average increase in RESTOM of the order 0.01 W m-2 is seen. However, there is more significant redistribution of shortwave cloud forcing over the Pacific Ocean. A 20th Century simulation is ongoing, and impacts will be reported here. The bug involves 3 lines (in bold below) in one subroutine: components/cam/src/physics/cam/micro_mg2_0.F90 ______________________________     do i=1,mgncol        ! conservation of rain number        !-------------------------------------------------------------------        ! Add evaporation of rain number.        if (pre(i,k) < 0._r8) then           dum = pre(i,k)*deltat/qr(i,k)           dum = max(-1._r8,dum)           nsubr(i,k) = dum*nr(i,k)/deltat        else           nsubr(i,k) = 0._r8        end if     end do
Code: 
<span style="caret-color: #333333; color: #333333; font-family: UbuntuRegular, Helvetica, Arial; font-size: 14px; white-space: normal;">______________________________</span>
 The intended behavior for these three lines is:[*]Calculate the fraction of rain mass that is being evaporated in the current time step.[*]Limit that fraction to no more than 1 (i.e. do not evaporate more rain than we actually have).[*]Evaporate the same fraction of the rain number.[/list]However, this code mixes quantities that are averaged over the grid cell, and those only covering the fraction of the cell with precipitation. The effect of the bug is to produce rain drops that are too small in some circumstances, and the correction will cause the particle size to increase.The limiter is redundant with both the mass conservation code above it (which prevents pre from being too large in the first place), and the number conservation code below it (which would limit nsubr anyway). The bug fix removes this redundant limiter, replacing all three lines with one line (in bold below):______________________________     do i=1,mgncol        ! conservation of rain number        !-------------------------------------------------------------------         ! Add evaporation of rain number.        if (pre(i,k) < 0._r8) then           nsubr(i,k) = pre(i,k)*nr(i,k)/qr(i,k)        else           nsubr(i,k) = 0._r8        end if     end do______________________________
 
mmills

mmills

CSEG and Liaisons
Staff member
Affected Releases CESM2.0.0A bug has been found in the release code of CESM2.0.0 regarding the evaporation of rain number in Morrison-Gettelman V2 (MG2) cloud microphysics. This bug has been fixed in the cam6_0_005 tag, which was checked in to the CAM development trunk on July 16, 2018. Testing in a coupled piControl simulation reveals the effects of fixing this bug to be very small in the global average. A global average increase in RESTOM of the order 0.01 W m-2 is seen. However, there is more significant redistribution of shortwave cloud forcing over the Pacific Ocean. A 20th Century simulation is ongoing, and impacts will be reported here. The bug involves 3 lines (in bold below) in one subroutine: components/cam/src/physics/cam/micro_mg2_0.F90 ______________________________     do i=1,mgncol        ! conservation of rain number        !-------------------------------------------------------------------        ! Add evaporation of rain number.        if (pre(i,k) < 0._r8) then           dum = pre(i,k)*deltat/qr(i,k)           dum = max(-1._r8,dum)           nsubr(i,k) = dum*nr(i,k)/deltat        else           nsubr(i,k) = 0._r8        end if     end do
Code: 
<span style="caret-color: #333333; color: #333333; font-family: UbuntuRegular, Helvetica, Arial; font-size: 14px; white-space: normal;">______________________________</span>
 The intended behavior for these three lines is:[*]Calculate the fraction of rain mass that is being evaporated in the current time step.[*]Limit that fraction to no more than 1 (i.e. do not evaporate more rain than we actually have).[*]Evaporate the same fraction of the rain number.[/list]However, this code mixes quantities that are averaged over the grid cell, and those only covering the fraction of the cell with precipitation. The effect of the bug is to produce rain drops that are too small in some circumstances, and the correction will cause the particle size to increase.The limiter is redundant with both the mass conservation code above it (which prevents pre from being too large in the first place), and the number conservation code below it (which would limit nsubr anyway). The bug fix removes this redundant limiter, replacing all three lines with one line (in bold below):______________________________     do i=1,mgncol        ! conservation of rain number        !-------------------------------------------------------------------         ! Add evaporation of rain number.        if (pre(i,k) < 0._r8) then           nsubr(i,k) = pre(i,k)*nr(i,k)/qr(i,k)        else           nsubr(i,k) = 0._r8        end if     end do______________________________
 
mmills

mmills

CSEG and Liaisons
Staff member
Yes, both of these issues are outstanding in CESM2.0.1.The CESM2 Supported Releases and Known Issues page shows that the micro_mg2_0.F90 has not been fixed. I have confirmed this by checking out the 2.0.1 code and examining the routine components/cam/src/physics/cam/micro_mg2_0.F90.I also created a BW1850 case and looked at the atm_in namelist. The emissions bug has not been fixed either.  
 
mmills

mmills

CSEG and Liaisons
Staff member
Yes, both of these issues are outstanding in CESM2.0.1.The CESM2 Supported Releases and Known Issues page shows that the micro_mg2_0.F90 has not been fixed. I have confirmed this by checking out the 2.0.1 code and examining the routine components/cam/src/physics/cam/micro_mg2_0.F90.I also created a BW1850 case and looked at the atm_in namelist. The emissions bug has not been fixed either.  
 
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