Can we run offline with 30 vertical layers rather than 56?

[sharp@mail_iap_ac_cn]

Dear everyone,

I want to run CESM 1.2.0 offline using MERRA dataset. Following the instrcutions in forum,I set the "CAM_CONFIG_OPTS" to "-phys cam5 -offline_dyn -nlev 56", but this nearly double the computing time compared with the default FC5 run. So to reduce the computing time, can we set the "CAM_CONFIG_OPTS" to "-phys cam5 -offline_dyn -nlev 30" with MERRA dataset which has a 72 vertical layers?

Best wishes for you and thanks in advance!

Zhang T.H.

 

[tilmes]

The offline version of the model has to be run with the number of levels in the meteorological data set, which is actually 56 instead of 72, running CAM. The extra levles that go over the model top are not used, and so you need to use -nlev 56.  However, if you want to really run the offline version with less levels, you will have to interpolate each of the meteorological data files to the levels you would like to use. You will also have to create a new initial condition file (nc_data) and you will also have to make sure that the model still performs reasonable and tuning may need to be applied.Simone 

 

[sharp@mail_iap_ac_cn]

Dear Simone,Thanks for your kind relpy.I have interpolated meteorological data files linearly to lev 30. The results show that the difference of dust burden between -nlev 56 and -nlev 30 offline runs is within 5%, so I think the model with -nlev 30 offline run performs reasonable, at least for dust.Additionally, the variable of ORO, orography flag,  in 2012 input meteorological data files are missing which are downloaded from https://www.earthsystemgrid.org. Actually, the model can run offline without it. I wonder whether the offline run read the ORO in meteorological data files or not and which variables in the meteorological data files are used by the offline run?Best wish for you!Zhang T. H.