Near-modern CESM1.0 | Atmosphere

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 [bnd_topo]

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.

Variable         

Description
solar_const Solar constant
ch4vmr CH4 volume mixing ratio
n2ovmr N2O volume mixing ratio
f11vmr CFC11 volume mixing ratio
f12vmr1 CFC12 volume mixing ration

1 For Pre-Industrial paleo experiments, F11VMR and F12VMR should be set to 0.