CESM 83-level Simulations

In the next generation of the Community Atmosphere Model (CAM7), the model top will be raised and the vertical resolution will be increased.  The model top will be approximately 80 km (compared to 40 km in older generations), and the grid spacing in the free troposphere and lower stratosphere will be reduced to about 500 m compared to around 1137m in older generations.  In addition to this, extra levels will be added to the boundary layer and the lowest model level will be lowered.  Overall, this "mid-top" version of CAM7 will have 93 levels.  However, many other changes will also be present in CAM7 such as physics updates and the new spectral element dynamical core, making it challenging to identify the role of this enhanced resolution in changes between CAM7 and CAM6.

This dataset consists of a suite of simulations that use CAM6 physics and the finite volume dynamical core, but with CAM7's grid except for the changes to the levels in the boundary layer i.e., an 83 level model.  The boundary layer levels are not changed because once those are changed, some re-tuning of the physical parameterizations is needed precluding a clean comparison and identification of the impact of vertical resolution.  Only minimal changes to CAM6 physics have been applied to these simulations; the non-orographic gravity wave drag scheme was turned on, the upper boundary condition was changed such that any remaining gravity wave momentum flux is deposited at the model lid, and some minor tuning of the gravity wave drag settings was also performed to optimize the behavior of the QBO.  These simulations can, therefore, be compared with existing CAM6 simulations to identify the impacts of this raising of the model lid and change to the resolution of the free troposphere and lower stratosphere.  These simulations have an internally generated QBO and a relatively good representation of the stratospheric polar vortices and can be used to explore climate variability and change in the presence of those features.

These simulations are described in Simpson et al "Toward the vertical resolution of the next generation of the Community Atmosphere Model", to be submitted to JAMES, and this manuscript should be cited when referring to them. 

DOI: 10.5065/S125-CA92

Project Details

  • Simulation Names:
    • Pre-industrial control: b.e21.B1850.f09_g17.L83_cam6.001
    • Coupled historical ensemble: b.e21.BHISTcmip6.f09_g17.L83_cam6.00X, X=1-3
    • Coupled SSP370 ensemble: b.e21.BSSP370cmip6.f09_g17.L83_cam6.00X, X=1-3
    • AMIP historical ensemble: f.e21.FHIST_BGC.f09_f09_mg17.L83_cam6.00X, X=1-3
    • AMIP SSP370 ensemble: f.e21.FHIST_BGC.f09_f09_mg17.L83_cam6_SSP370.00X, X=1-3
  • Model Version: CESM2.1.2 Codebase | Documentation
  • Resolution: 0.9x1.25_gx1v7 (CESM nominal 1o grid)
  • Years: 1-105 (pre-industrial control), 1850-2014 (coupled historical), 2014-2100 (coupled SSP370), 1979-2014 (AMIP historical), 2015-2020 (AMIP SSP370)
  • Ensemble Size: 1 member (pre-industrial control), 3 members (coupled and AMIP historical, coupled and AMIP SSP370)
  • Time Frequencies Saved: Monthly, Daily
  • Machine: NCAR:Cheyenne
  • Compsets: B1850 (pre-industrial control), BHISTcmip6 (coupled historical), BSSP370 (coupled SSP370), FHIST_BGC (AMIP historical and SSP370), all compsets had extensive modifications
  • Forcings: All simulations follow the CMIP6 forcing protocols for the forcing that is evolving.

  • Namelist settings: The following gravity wave settings were used.  To reproduce the climate of these simulations, these should be entered into user_nl_cam

    use_gw_rdg_beta=.true.
use_gw_convect_dp=.true.
use_gw_front=.true.
effgw_cm = 1.D0
gw_drag_file = '$DIN_LOC_ROOT/atm/waccm/gw/newmfspectra40_dc25.nc'
gw_polar_taper = .true.
gw_top_taper = .false.
pgwv = 32
effgw_beres_dp               = 0.90D0
gw_qbo_hdepth_scaling                = 0.25D0
qbo_use_forcing              = .false.
tau_0_ubc=.true.
frontgfc               = 2.7D-15
taubgnd                = 2.5D-3
effgw_rdg_beta = 0.75D0
effgw_rdg_beta_max = 0.75D0
!---additional gravity wave settings to make it look like SC-WACCM
gw_apply_tndmax                = .false.
gw_limit_tau_without_eff               = .true.
gw_lndscl_sgh          = .false.
gw_oro_south_fac               = 2.d0
fv_nsplit   =            16
fv_nspltrac =            8
fv_nspltvrm =            8

  • Case setup: The historical L83 cases were set up using the following create_newcase command.  Since the 83 level configuration is not available by default, an xmlchange command is needed to change the number of levels to 83 as follows.

    ./create_newcase --case $casedir --res f09_g17 --compset FHIST_BGC --run-unsupported
cd $casedir
./xmlchange --apend --file env_build.xml -d CAM_CONFIG_OPTS --val="-nlev=83"
  •  Initialization: The simulations will then need to be initialized from an atmospheric initial state that is on those 83 levels.  This can achieved by interpolation onto the levels described by the hybrid coefficients in this file.  If you have access to NCAR computers, the restart files from the 1850 pre-industrial control that were used to initialize the coupled historical simulations are located at /glade/campaign/cesm/development/cvcwg/cvwg/L83/restarts/b.e21.B1850.f09_g17.L83_cam6.001 These files are available by contacting the CVCWG liaisons for assistance.

Data Acquisition

The pre-industrial control is only available on NCAR's casper system. If you do not have access to NCAR's casper machine you can contact the CVCWG liaisons for assistance. All other data is available on both the NCAR Research Data Archive (Web Access) and NCAR's casper system (NCAR Internal). 

  • NCAR Internal

    Location on NCAR's campaign store or on the NCAR machine casper:

    /glade/campaign/cesm/development/cvcwg/cvwg/L83/timeseries/ 

  • Web Access

    All simulations but the pre-industrial control are available from NCAR's Research Data Archive. The following are step by step directions on how to download this data from the Climate Data Gateway.

    1. Proceed to the CESM2 83-level simulations.
    2. Click on the Data Access tab, and click on the component and time frequency you are interested in.
    3. All variable files for the component and time frequency are shown. Use the filter option at the top to narrow down the file listing.
    4. Click the box next to each file you would like to download. Once a file has been selected, you will see download option boxes above the file listing. Download methods include: CSH Download Script, Python Download Script, Jupyter Notebook Download Script, or GLOBUS Download. Click on the method you would like to use to proceed.