CESM1 Paleo Users Guide

Deep Time CESM1

Deep time paleo climate simulations encompass time periods where the continents are in different global configurations than present day.  Paleo modelers are required to provide two netCDF files with topography/bathymetry and land use (vegetation) on a regular latitude/longitude grid (e.g., 2ox2o), using lat(lat) and lon(lon) as coordinate variables.

Overview presentation - Christine Shields

Flowchart - Nan Rosenbloom

topobathy.nc

The topobathy.nc netCDF file should contain topography and bathymetry on a regular latitude/longitude grid (e.g., 2ox2o). Positive values represent height above sea level and negative values represent ocean bathymetry. The topobathy.nc defines your land/ocean mask.

  • netCDF format
  • Coordinate variables:  lat(lat), lon(lon)
  • longitude: 0 to 360o
  • latitude: -89 to 89o

vegetation.nc

The vegetation.nc netCDF file should contain land use (i.e., vegetation) on a regular latitude/longitude grid (e.g., 2ox2o).

  • netCDF format
  • Coordinate variables:  lat(lat), lon(lon)
  • longitude: 0 to 360o
  • latitude: -89 to 89o

For most deep time paleo simulations, we assign LSM (Land Surface Model) land-use types for each grid point and then convert these LSM types to CLM3 (Community Land Model) surface information (Appendix 8.6) using the tool paleo_mkraw.csh.  Because CLM3 requires a complicated array of surface information for each grid cell, whereas LSM uses a simple integer value to represent land-use at each grid point, assigning an LSM integer value and using the paleo_mkraw.csh tool to convert to LSM types to CLM3 format provides a simple method to create surface data information for deep time. 

Modelers may first need to construct LSM land cover maps from biome maps using the LSM definitions listed in the Appendix 8.5.  The CLM3 PFTs definitions used in paleo_mkraw.csh are listed in Appendix 8.6.

LSM land-use types are used in paleo_mkraw.csh because LSM was the predecessor to CLM3 and used in CSM1.4.  If this does not suite your needs, you will need to modify paleo_mkraw.csh to convert from your preferred land-use type structure to CLM3 surface data information.