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how to make ensemble runs using CESM1.2
- Thread starter 2013asz8013@gmail_com
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- cesm1.2
Hi @jedwards, Thank you for your guidance! I am trying to conduct ensemble runs using CESM2.1. I am wondering could you direct me to the instructions? I could not find related threads in the forum.CESM2 has capability to generate ensemble members and cylc workflow control files for running ensembles, however there is nothing like this in cesm1.2.
Many thanks for the quick reply! I am wondering if I need to add different pertlim values to each of the user_cam_nl files created by ./creat_clone --ensemble?In cesm2.1.3 ./create_clone has options --ensemble and --keep-exe which will aid in creating an ensemble of cases.
cime/scripts/Tools/generate_cylc_workflow.py will create a suite.rc file that can be used with the workflow control tool cylc
Thanks again for the guidance! I guess I still have to add the pertlim to individual cases manually. :)Yes - that would be the normal process for creating an ensemble.
H
Because I am new to CESM, I am wondering whether two hybrid runs with the same reference case, the same start date, and the same pertlim value produce the same outputs (bit-to-bit results)?
Thank you so much for your help!
Hi @jedwards,Yes - that would be the normal process for creating an ensemble.
Because I am new to CESM, I am wondering whether two hybrid runs with the same reference case, the same start date, and the same pertlim value produce the same outputs (bit-to-bit results)?
Thank you so much for your help!
Hi jedwards,On the same machine with the same compiler and pe-layout, yes they should give bfb results.
Do ensemble members have to be hybrid run? I wonder if it is okay to clone an existing case and do another startup run with pertlim specified in user_nl_cam? Thanks!
Hi Hannay,The first method I pointed you to (varying pertlim in the CAM namelist) is a very common an recognized method to create ensemble runs.For instance, it what was used to create the Large ensemble done at NCAR.See: http://www2.cesm.ucar.edu/models/experiments/LENSIt is an ensemble of 30 runs created using round off error introduced through the CAM namelist (i.e. varying pertlim)http://www2.cesm.ucar.edu/models/experiments/LENS/instructionsThey varied pertlim from pertlim = 1.d-14, 2.d-14, ..., 30.d-14to create their 30 ensemble members. I am not very familiar with the multi instance. To my knowledge, it is used for data assimilation but not really to create traditionnal ensemble.See: http://www.cesm.ucar.edu/models/cesm1.2/cesm/doc/usersguide/x834.html
Thanks for your reply and information! I am also learning how to do the ensemble simulations using CESM1.2 but I still do not understand the values assigned to pertlim. For example, 1.d-14, what does "1" "d-14" mean here? Does the former refer to the realization of the ensemble member?
Best,
Li
Ok. Thanks jedwards!Li that is a representation of the value 0.00000000000001 - and that is the perturbation to be added to the initial condition of the T field.
Hi jedwards, can I use such small perturbation in a short term run, for example six month, i.e. whether the perturbation would lead to obvious internal variability among ensemble members through several months integration?Li that is a representation of the value 0.00000000000001 - and that is the perturbation to be added to the initial condition of the T field.