Near-modern climate simulaitons | Coupler

To simulate changes in solar irradiance through time, the model calculates the eccentricity, obliquity and precession based on Berger et al., 1993.  The model sets these parameters automatically using a variable called orb_year, which is set in the coupler namelist (cpl.buildnml_prestage.csh) and is defined in years before 1950.


          a. AD values, i.e. 1800, 1900, 1950, 1990, 2000, etc.

  • should be expressed with the explicitly named year.

          example: orb_year = 1800

          b. BC values, i.e. 10ka, 130ka, 506ka

  • should be expressed in years relative to 1950 (1950 - <time period of interest>)


o        506ka BP:      orb_year = (1950 - 506ka) = -504050

o        4ka BP:         orb_year = (1950 – 4000) = -2050


Since we have no good estimate of the orbital variations beyond ~1Ma BP, eccentricity, obliquity, and the moving vernal equinox must be expressed individually for pre-Quaternary experiments.  Details on how these variables are computed can be found by reviewing the code in the CCSM3 csm_share subdirectory.