CCSM3.0 Paleo UG | Near-modern climate simulations | Atmosphere

The atmospheric model in CCSM3 is the Community Atmosphere Model 3.0 (CAM3). 

If you change the land surface elevation from present day (e.g., increasing the height of the Greenland Ice Sheet, or lowering the Rocky Mountains) you must create a new topography file for the atmosphere model (CAM3) that reflects these changes. 

Surface topography in CCSM3 is parameterized by the CAM3 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]


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 outfile

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 CCSM3 present-day base topography (; distributed in setup_tools.tar).


If atmospheric initial conditions are completely unknown we provide an ncl tool (cami_create_ccsm3.csh) that will create an initial file (CAMI) 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.

CAM3 Namelist options [cam.buildnml_prestage.csh]

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 CCSM3 experiment, and not in the CAM3 namelist. This is different from CAM stand-alone or CAM-SOM runs.

SCONSolar constant
CO2VM2CO2 volume mixing ratio
CH4VMRCH4 volume mixing ratio
N20VMRN2O volume mixing ratio
F11VMR1CFC11 volume mixing ratio
F12VMR1CFC12 volume mixing ration

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

B:  Atmospheric Forcing Files

  • Absorption/Emissivity: [absdata]
  • The present day absorption/emissivity forcing dataset was built with wide constraints and is therefore flexible and can be used for paleoclimate cases.
    •  [CCSM3.0 Release DEFAULT]
  • Ozone: [bndtvo]
  • Typically, present day or pre-industrial ozone mixing ratio boundary forcing files are used for paleoclimate cases.  Ozone forcing files are independent of resolution.
    •   [CCSM3.0 Release DEFAULT)
    •  [Pre-Industrial]
  • Aerosols: [aeroptics][bndtvaer]
  • Pre-industrial or present day aerosol mass files are resolution dependent.  We provide T31 and T42.  Please contact the Paleo Liaison if you need a different resolution.
    •    [CCSM3.0 DEFAULT]
    •   [CCSM3.0 DEFAULT]
    •  [Pre-Industrial]