7. Challenge: Run an LGM simulations with the Paleoclimate-Calibrated CESM2

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7. Challenge: Run an LGM simulations with the Paleoclimate-Calibrated CESM2#

Tutorials at the 2025 paleoCAMP | June 16–June 30, 2025

Jiang Zhu
jiangzhu@ucar.edu
Climate & Global Dynamics Laboratory
NSF National Center for Atmospheric Research

Learning Objectives:

  • Showcase how a complicated paleo simulation is done.

  • Still four steps(!), but with more XML and namelist changes to apply the paleoclimate boundary conditions.

  • Be aware that many efforts went to develop the LGM boundary conditions(not shown here), which may take months.

  • Reference CESM2-PaleoCalibr LGM simulation

Time to learn: 20 minutes

How to get started?

Use terminal from your system directly

ssh -XY YOUR_SUERNAME@derecho.hpc.ucar.edu

Type in your CIT password (the one you set up with CISL) and approve the DUO push

Derecho SSH

Create new case#

  • A long-format compset was used to have more precise control of how I want to run each component

cd /glade/campaign/cesm/development/palwg/cesm_tags/cesm2.1.5/cime/scripts
./create_newcase --case ~/b.e21.B1850.f19_g17.PaleoCalibr.21ka.02 --res f19_g17 --compset 1850_CAM60_CLM50%SP_CICE_POP2_RTM_SGLC_SWAV --run-unsupported

case setup#

  • I have FORTRAN code changes that need to be put into SourceMods/src.xxx/

  • I specify how many CPUs to use for each component for a better computation performance

  • Lots of xmlchange to take care of the different land sea distribution due to the lowered sea level at the LGM

cd ~/b.e21.B1850.f19_g17.PaleoCalibr.21ka.02

cp /glade/work/jiangzhu/data/inputdata/cesm2_21ka/gx1v7_overflow    SourceMods/src.pop/
cp /glade/work/jiangzhu/data/inputdata/cesm2_21ka/gx1v7_region_ids  SourceMods/src.pop/
cp /glade/u/home/jiangzhu/cesm/backup/nimax_limiterA/micro_mg2_0.F90 SourceMods/src.cam/micro_mg2_0.F90

./xmlchange NTASKS_CPL=1024,NTHRDS_CPL=1,ROOTPE_CPL=0
./xmlchange NTASKS_ATM=1024,NTHRDS_ATM=1,ROOTPE_ATM=0
./xmlchange NTASKS_LND=384,NTHRDS_LND=1,ROOTPE_LND=0
./xmlchange NTASKS_GLC=384,NTHRDS_GLC=1,ROOTPE_GLC=0
./xmlchange NTASKS_ROF=384,NTHRDS_ROF=1,ROOTPE_ROF=0
./xmlchange NTASKS_ICE=640,NTHRDS_ICE=1,ROOTPE_ICE=384
./xmlchange NTASKS_OCN=256,NTHRDS_OCN=1,ROOTPE_OCN=1024
./xmlchange NTASKS_WAV=256,NTHRDS_WAV=1,ROOTPE_WAV=1024

./xmlchange RUN_TYPE=startup
./xmlchange GET_REFCASE=FALSE

./xmlchange ATM_DOMAIN_PATH=/glade/work/jiangzhu/data/inputdata/cesm2_21ka
./xmlchange LND_DOMAIN_PATH=/glade/work/jiangzhu/data/inputdata/cesm2_21ka
./xmlchange OCN_DOMAIN_PATH=/glade/work/jiangzhu/data/inputdata/cesm2_21ka
./xmlchange ICE_DOMAIN_PATH=/glade/work/jiangzhu/data/inputdata/cesm2_21ka
./xmlchange ATM_DOMAIN_FILE=domain.lnd.fv19_gx1v7_21ka.200623.nc
./xmlchange LND_DOMAIN_FILE=domain.lnd.fv19_gx1v7_21ka.200623.nc
./xmlchange OCN_DOMAIN_FILE=domain.ocn.fv19_gx1v7_21ka.200623.nc
./xmlchange ICE_DOMAIN_FILE=domain.ocn.fv19_gx1v7_21ka.200623.nc

./xmlchange ATM2OCN_FMAPNAME=/glade/work/jiangzhu/data/inputdata/cesm2_21ka/map_fv19_TO_gx1v7_21ka_aave.200623.nc
./xmlchange ATM2OCN_SMAPNAME=/glade/work/jiangzhu/data/inputdata/cesm2_21ka/map_fv19_TO_gx1v7_21ka_blin.200623.nc
./xmlchange ATM2OCN_VMAPNAME=/glade/work/jiangzhu/data/inputdata/cesm2_21ka/map_fv19_TO_gx1v7_21ka_patc.200623.nc
./xmlchange OCN2ATM_FMAPNAME=/glade/work/jiangzhu/data/inputdata/cesm2_21ka/map_gx1v7_21ka_TO_fv19_aave.200623.nc
./xmlchange OCN2ATM_SMAPNAME=/glade/work/jiangzhu/data/inputdata/cesm2_21ka/map_gx1v7_21ka_TO_fv19_aave.200623.nc
./xmlchange ROF2OCN_FMAPNAME=/glade/work/jiangzhu/data/inputdata/cesm2_21ka/map_r05_nomask_TO_gx1v7_21ka_aave.200623.nc
./xmlchange ROF2OCN_LIQ_RMAPNAME=/glade/work/jiangzhu/data/inputdata/cesm2_21ka/map_r05_TO_gx1v7_21ka_merged_200623.nc
./xmlchange ROF2OCN_ICE_RMAPNAME=/glade/work/jiangzhu/data/inputdata/cesm2_21ka/map_r05_TO_gx1v7_21ka_nnsm_200623.nc

./case.setup

case build#

  • I usually set up namelist changes before running case.build

  • user_nl_cpl: orbital change

orb_iyear   = -19050
orb_mode    = 'fixed_year'

  • user_nl_cam: GHG, topography with added ice sheets, and model cloud parameter tuning

bnd_topo    = '/glade/work/jiangzhu/data/inputdata/cesm2_21ka/bnd_topo_fv_1.9x2.5_LGM_c200629_nc3000_Nsw084_Nrs016_Co120_Fi001.replaced.nc'
scenario_ghg= 'FIXED'
co2vmr      = 190e-6
ch4vmr      = 375e-9
n2ovmr      = 200e-9
f11vmr      = 0.0
f12vmr      = 0.0

micro_mg_num_steps  = 8
dust_emis_fact      = 0.55D0
clubb_gamma_coef    = 0.275D0

  • user_nl_pop changes: ocean bathymetry, land-sea mask, and initial condition

topography_file     = '/glade/work/jiangzhu/data/inputdata/cesm2_21ka/topography_21ka_200623.ieeei4'
region_mask_file    = '/glade/work/jiangzhu/data/inputdata/cesm2_21ka/region_mask_21ka_200623.ieeei4'
ebm_param_option    = 'internal'

init_ts_file        = '/glade/work/jiangzhu/data/inputdata/cesm2_21ka/b.e12.B1850C5.f19_g16.i21ka.03.pop.h.0801-0900.climo.ncra.nc'
init_ts_file_fmt    = 'nc'
init_ts_option      = 'file'
init_iage_init_file = '/glade/work/jiangzhu/data/inputdata/cesm2_21ka/b.e12.B1850C5.f19_g16.i21ka.03.pop.h.0801-0900.climo.ncra.nc'
init_iage_init_file_fmt = 'nc'
init_iage_option    = 'file'
overflows_restfile  = 'b.e21.B1850.f19_g17.PaleoCalibr.21ka.02.pop.ro'

  • user_nl_clm: land surface data change to reflect the LGM ice sheets, and remove anthropogenic processes

fsurdat = '/glade/work/jiangzhu/data/inputdata/cesm2_21ka/surfdata_fv19_hist_16pfts_nourb_CMIP6_21ka.c200624.nc'
finidat = '/glade/work/jiangzhu/data/restart/i.e21.I1850C5.f19_g17.21ka.01/i.e21.I1850C5.f19_g17.21ka.01.clm2.r.1401-01-01-00000.nc'

urban_hac='OFF'
calc_human_stress_indices='NONE'
do_harvest=.false.
stream_year_first_urbantv=1850
stream_year_last_urbantv=1850
irrigate=.false.
popdensmapalgo = 'nn'

  • user_nl_rtm: initial condition for river is being set here

finidat_rtm = '/glade/work/jiangzhu/data/restart/b.e12.B1850C5.f19_g16.i21ka.03/0901-01-01/b.e12.B1850C5.f19_g16.i21ka.03.rtm.r.0901-01-01-00000.nc'
rtm_effvel  = 'NULL'

  • user_nl_cice: bathymetry for the sea ice model, as well as the initial condition

kmt_file    = '/glade/work/jiangzhu/data/inputdata/cesm2_21ka/topography_21ka_200623.ieeei4'
ice_ic      = 'default'

./case.build

submit job#

  • The model runs 46 years per wallclock day, so STOP_N=20 works well (20 years can be finished within the limit of JOB_WALLCLOCK_TIME of 12 hours)

./xmlchange STOP_OPTION=nyears,REST_OPTION=nyears
./xmlchange STOP_N=20,REST_N=10
./xmlchange RESUBMIT=4
./xmlchange JOB_WALLCLOCK_TIME=12:00:00
./case.submit
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