A user can add there own variables at any time to the
script. The new variables can be something extracted
directly from the WRFOUT file, processed with the WRF-ARW NCL
tools, or calculated within the script. Content must be
added to several sections within the wrfout_to_cf.ncl script
when adding a new variable. This instructional will
present an outline of the work that needs to be done.
Create and set a variable
A flag needs to be set to specify
that the variable is to be included in the output file.
The variables are categorized into larger sets of variables
(out2dMet, out2dRadFlx, out2dLandSoil, outPressure, outEta,
outSoil). Determine the category that the new variable
best fits and place the flag for the output variable in that
category. For example the variable ws_10m is placed in the
category out2dMet and given the flag:
out2dMet@ws_10m. The category (e.g. out2dMet) and the
variable (out2dMet@ws_10m) must both be set to True for the
variable to be included in the output file.
Set the variable contents:
The location for retrieving /
calculating a variable is divided by the variable type and the
method to assign the variable to the data. For example,
all out2dMet fields retrieved directly from the WRFOUT file are
placed together within the script. Another example is that
all calculated values on eta levels are placed together.
Determine the best corresponding location to insert the new
variable. Make sure that it is placed within the larger
category of variables (e.g. out2dMet) to be processed.
Refer to any number of variables within the script for examples
as to how this can be done.
Delete the time attribute - Eta level output only:
After assigning the data t the variable the CF attributes must
be set for the new variable. The CF attributes are
determined by using the CF documentation (see the Variables
page). The key attributes are: long_name,
standard_name, and units. The variable attributes are
assigned by calling the internal procedure:
Add the new variable to be outputted to the post-processed
For some reason the attribute time is included with all of the
eta level variables. If a new eta level variable is
used/created, that variable has to be included to have the time
The last step in adding a new
variable is to include the variable in the output file.
Find the section where the data is written to the wrfpost file
that corresponds to the category of variables (e.g.
out2dMet). Add a new if-then sequence to include the new
variable. The outputted variable is dimensioned based on
the spatial and temporal subsetting.
The best method to add a new
variable is to identify a similar variable that is currently in
the script. The similarities are based on the type of
variable and the how the variable is retrieved and/or
calculated. Then follow that variable through the script
to see how it is handled.