Setting orbital parameters in ESM1.5

Earth System Earth System Model
1

Hi everyone,

The versions 1.2 of the ESM1.5 configurations add the ability to control orbital parameters at runtime through a UM namelist. In particular, the following variables can be set from the main atmosphere namelist:

  • ECCENTRICITY: The eccentricity of Earth’s orbit.
  • OBLIQUITY_RAD: The obliquity of the Earth, in radians.
  • DAY_PERIHELION: The time of the perihelion passage, in days.
  • LON_PERIHELION_RAD: The longitude of the perihelion, in radians.

These notes detail how to set these parameters.

After cloning one of the available configurations:

locate the atmosphere/namelists file contained in the control directory. A new optional namelist group &ASTRON_PERIODIC containing the above variables can then be added. For example, to specify orbital parameters suitable for a 49ka experiment, we can add

 &ASTRON_PERIODIC
 ECCENTRICITY=0.01292,
 OBLIQUITY_RAD=0.42647599,
 DAY_PERIHELION=323.7698,
 LON_PERIHELION_RAD =1.08997557,
 /

It doesn’t matter where the &ASTRON_PERIODIC group appears relative to the other namelist groups. However, note that aside from adding the new group, the order of the existing namelist groups should not be modified.

The &ASTRON_PERIODIC group can also be left out from the namelist file, in which case the model will default to the modern values used in previous releases:

&ASTRON_PERIODIC
 ECCENTRICITY=1.6710222E-02,
 OBLIQUITY_RAD=0.409092804,
 DAY_PERIHELION=2.667,
 LON_PERIHELION_RAD =1.7967674211761814
/

Feel free to ask any questions or let us know if you run into any problems with these changes!

Thanks @HIMADRI_SAINI for sharing the 49ka parameters used for testing during development.

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