Adding CAM output variable#
A common source code modification that you may want to do is to output a new variable that is not already defined as an output variable in CESM.
As an example, we will add a new variable to CAM: the atmospheric temperature at 750hPa.
Adding an output variable to CAM#
CAM has a history field that corresponds to the temperature at 500hPa and a number of other pressure levels, but not at 750hPa. Suppose you wanted to output the temperature at 750hPa. The following two calls are required to add an output variable:
call addfld('T750',...) (Add a field to the master field list)
call outfld('T750',...) (Collect values for this field and write to history file)
Each of these are now described in more detail:
addfld
#
The sub-routine addfld
adds a field to the master list with the following syntax:
addfld(fname,type,avgflag,units,long_name)
where
fname
= field nametype
= the type of field. The entry for a single level field would be “horiz_only” and the entry for a 3D field would be “(/ ’lev’ /)”.avgflag
= Averaging flag, A = average, I=instantaneousunits
= the units of the fieldlong_name
= Field full name
Appropriate values of these parameters for the output of T750 are:
call addfld('T750',horiz_only, 'A', 'K', 'Temperature at 750hPa pressure surface')
outfld
#
The subroutine outfld
accumulates (or takes the minimum or maximum of, as appropriate) the field into the history buffer for the appropriate history tape with the following syntax
outfld(fname, field, idim, c)
with
fname
= Field namefield
= array containing field valuesidim
= longitude dimension of field arrayc
= chunk (physics) or latitude (dynamics) index.
For example:
call outfld(’T750’,t750, pcols, lchnk)
add_default
#
Another useful subroutine is the subroutine add_default
. The subroutine add_default
Add a field to the list of default fields on history file with the following syntax
subroutine add_default (fname, tindex, flag)
where
fname
= Field nametindex
= history tape indexflag
= Averaging flag: A = average (default). I = instantaneous
For example:
call add_default ('T750', 1, ' ')