[Go-essp-tech] CMOR and cell_measures issues

[Bentley, Philip]

Hi Karl,
 
A somewhat belated follow-up question in connection with this proposal
(and with some slight overlap with Jamie's email which crossed on the
ether)...
 
As things stand the files named in the 'associated_files' attribute
appear thus (using our RCP 4.5 simulation as an example):
 
"... gridspecFile: gridspec_fx_HadGEM2-ES_rcp45_r0i0p0.nc areacella:
areacella_fx_HadGEM2-ES_rcp45_r0i0p0.nc"
 
Are the <expt_id>_<rip> parts (i.e.  'rcp45_r0i0p0.nc' ) actually
required? AFAIK, our gridspec/cellarea files will not change from one
simulation to the next using the same model (HadGEM2-ES in this case).
 
Since, like most centers, we will be running large numbers of
simulations using the same model, it looks like we would need to create
numerous duplicates of the gridspec/cellarea files - or lots of symlinks
- in order to for these references to make sense. Unless you are
planning to manage that on our behalf somehow...?
 
I think our 4 gridspec files for the HadGEM2 atm grids are likely to be
called something like...
 
gridspec_fx_HadGEM2-ES_atm_pgrid.nc  
gridspec_fx_HadGEM2-ES_atm_ugrid.nc 
gridspec_fx_HadGEM2-ES_atm_vgrid.nc 
gridspec_fx_HadGEM2-ES_atm_uvgrid.nc 
 
So without any simulation-specific info. (There would also be files for
the ocean grids)
 
As it happens the gridspec files contain grid cell areas, so I'm now
wondering if we'd even supply both?
 
I'd be interested to hear your thoughts on this. I may be
mis-understanding something/everything :-)
 
Regards
Phil
 


________________________________

	From: Karl Taylor [mailto:taylor13 at llnl.gov] 
	Sent: 19 October 2010 18:36
	To: martin.juckes at stfc.ac.uk
	Cc: Bentley, Philip; Doutriaux, Charles; Kettleborough, Jamie;
Bryan Lawrence; cmor at lists.llnl.gov; go-essp-tech at ucar.edu;
Kyle.Olivo at noaa.gov
	Subject: CMOR and cell_measures issues
	
	
	Dear CMOR users,
	
	It has been brought to our attention that the CF checker (which
is different from the CMOR checker) traps an error in CMOR-produced
files indicating non-compliance with the CF conventions.  The error is
that the cell_measures attribute is defined, but the area and/or volume
data is not contained in the file.  [We have included a non-CF attribute
called "associated_files" that points to the files containing
area/volume.]  Still, in order to not confuse CF-compliant software we
plan to immediately release a new version of CMOR in which the
"cell_measures" attribute is replaced by a non-CF attribute named
"ext_cell_measures" (indicating that the area/volume data is externally
available).
	
	Also, some groups have reported that not all their variables are
carried on the same grid.  (For example, sometimes the u and v fields
are staggered relative to T.)  In this case it would be necessary to
have more than one set of areas associated with the model, and this is
not currently possible since only areacella, areacello, and volcello are
defined in the CMIP5 request for model output.  We have therefore
decided to include an option for CMOR users to suppress writing of the
ext_cell_measures attribute when it would point to areacella or
areacello incorrectly.  The user would in effect be allowed one set of
areas to be associated with the atmospheric model and one set of
areas/volumes to be associated with the ocean models.  The user would
suppress the ext_cell_measures attribute (and areacella, areacello,
volcello would not appear in the "associated_files" attribute) for any
variables where these areas/volumes would be incorrect.
	
	We hope this is acceptable.
	
	Best regards,
	Karl and Charles
	
	
	

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