Deep Time CESM1 | Atmosphere

As a deep time modeler, you are responsible for creating a new topography file which you will point to in the user_nl_cam namelist.  You also specify trace gas constituents and the solar constant in user_nl_cam, if they differ from pre-industrial. The CESM User Guide describes the user namelist functionality in CESM1. 

bnd_topo:  topography

The atmosphere component model requires initial boundary conditions, including fractional landcover (LANDFRAC), topography (PHIS), surface roughness, (SGH), and high resolution surface roughness (SGH30), and an aerosol scaling factor (LANDM_COSLAT).  For deep time, surface roughness is approximated by multiplying the surface topography by 0.3 and 0.1, respectively.  

src: mk_bnd_topo_paleo.ncl

NOTE:  Angular, highly variable topography can cause instability in the CAM atmosphere model that is difficult to detect but may cause the model to crash without errors.  We recommend that you smooth your high resolution (10min) topography to reduce the likelihood of model instabilities.  We provide a rudimentary smoothing program for this purpose. The code allows you to set the number of smoothing passes (niter) you make over your initial topography, and produces a latitudinal cross section for comparison.



ncdata:  initial state

You can initialize your deep time simulation from a default cesm initial file (e.g.,, by setting the the ice initial condition to zero in the ice model namelist (user_nl_cice:  ice_ic='none').

Solar constant and trace gases 

Variable     Description
solar_constSolar constant
co2vmrCO2 volume mixing ratio
ch4vmrCH4 volume mixing ratio
n20vmrN2O volume mixing ratio
f11vmr1CFC11 volume mixing ratio
f12vmr1CFC12 volume mixing ration

 1 For deep time paleo experiments, F11VMR and F12VMR should be set to 0.



Other atmoshere forcing files:

  • Absorption/Emissivity:
  • The present day absorption/emissivity forcing dataset was built with wide constraints and is therefore flexible and can be used for paleoclimate cases.
    •   [CESM1.0 DEFAULT]
  • Ozone:
  • Typically, present day or pre-industrial ozone mixing ratio boundary forcing files are used for paleoclimate cases. Choice of dataset will depend on your control experiment.
    •   [CESM1.0 DEFAULT]