The atmospheric model in CESM1 is the Community Atmosphere Model (CAM5).
Changes to topography
If your scientific problem requires a change to land surface elevation from present day (e.g., increasing the height of the Greenland Ice Sheet, lowering the Rocky Mountains, etc.) you must create a new topography file for the atmosphere model that reflects these changes. Surface topography in CESM is parameterized by the CAM variable PHIS (surface geo-potential [m2/s2]), which is defined by the relationship:
- PHIS [m2/s2] = elevation[m] × gravity [m/s2]
- PHIS ÷ 9.81 m/s2 = elevation [m]
Topographic boundary conditions (PHIS, SGH, SGH20, LANDFRAC, LANDM_COSLAT) are defined in the file referenced by the 'topo_bnd' namelist variable in user_nl_cam. SGH30 is a new field.
Definesurf is a fortran-based tool designed to create a new topography input file. Near-modern paleo modelers can use definesurf by providing a netCDF file of their paleo topography at 10min resolution.
Usage: definesurf -t topofile -g gridfile -l landm_coslat.nc outfile
e.g.: definesurf -remap -t topo_lgm21ka_10min.sm9.nc -g /glade/p/cesm/cseg/mapping/grids/fv0.9x1.25_070727.nc -l /fis/cgd/cseg/csm/inputdata/atm/cam2/hrtopo/landm_coslat.nc topo_lgm21ka_re
Users are advised to create their new topography file by first creating an anomaly map of their time period relative to present day (ΔZ = topomy_TOPO_paleo– topomy_TOPO_present-day) and then adding this anomaly (ΔZ) to the CESM present-day base topography.
Initial Conditions [cam.i]
If atmospheric initial conditions are completely unknown we provide an ncl tool (cesm_cami_create.csh) that will create an initial file that will reflect a basic physical atmospheric state suitable for initialization that allows the atmospheric model to spin-up during the first few decades of integration. This tool is primarily used for Deep-Time modeling.
CAM Namelist options [user_nml_cam]
This section describes the namelist parameters that control aspects of your physical boundary forcing.
A: Solar constant and trace gases
You must assign appropriate values for the solar constant and for trace gas concentrations.
Note: Orbital parameters (as opposed to the solar constant) are set in the coupler namelist for a fully coupled CESM1 experiment.
||CH4 volume mixing ratio
||N2O volume mixing ratio
||CFC11 volume mixing ratio
||CFC12 volume mixing ration
1 For Pre-Industrial paleo experiments, F11VMR and F12VMR should be set to 0.