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How to disturb initial values to generate ensemble simulations



I am running the case esm-ssp585 (CESM2.1.3 version) and selected b.e21.BHIST_BPRP.f09_g17.CMIP6-esm-hist.002 as the reference case for initialization. If I want to do an ensemble simulation (say 20 simulations) by disturbing initial values, how can I do that? Thank you!


CSEG and Liaisons
Staff member
Hi Eric, I checked in with one of our CMIP scientists and she suggested this:

There are two ways to perturb an ensemble. It sounds like this user wants #2 (micro perturbation) but I'll list both just in case.

Macro perturbation: launch each ensemble member from a different year of the reference case
Micro perturbation: introduce a small perturbation to the atmospheric temperature field 'pertlim'. To simplify, I like to set the perturbation equal to the member number. Note that pertlim will only be recognized in a startup or hybrid run.

Add this line to user_nl_cam in the $CASEROOT:
pertlim = ${mbr}.d-14