The Runtime I/O Option

WRF’s Runtime I/O option allows output modification - to specify variables to add, remove, or output at different frequencies - without having to change the Registry, or to recompile.

This exercise teaches the process for increasing the frequency of variables, and to output additional variables not typically in the history files.

If you have existing wrfinput_d01 and wrfbdy_d01 files from a previous case, WPS pre-processing can be skipped. If not, return to the Single Domain exercise and generate these files again.

Increase the Frequency of WRF Output Variables

Use the “Runtime I/O” option to increase the frequency of the following variables. They will be saved to a separate file - not the standard history (wrfout*) files.

• RAINC : Total accumulated cumulus precipitation

• RAINNC : Total accumulated grid-scale precipitation

• T2 : Temperature at 2m

• Q2 : Water vapor at 2m

1. Edit namelist.input to add the below settings. Tip: Start with the namelist set up for the Single Domain Run.

   
   

   &time_control
   restart_interval = 72000
   iofields_filename = "myoutfields_d01.txt",
   io_form_auxhist24 = 2,
   auxhist24_interval = 30,
   
   &domains
   max_dom = 1
   

   
   

   Note

   The above namelist settings instruct wrf.exe to read a file called myoutfields_d01.txt and output its data to a new, unused stream (24). io_form_auxhist24 = 2 specifies netCDF output every 30 simulation minutes (auxhist24_interval=30). Set restart_interval to a large value to avoid writing a restart file - while outputting a restart file is good practice in the real world, it is unnecessary for this class.

   
   
   
   
   
   

2. Create and then save file called myoutfields_d01.txt in the wrf/test/em_real directory. Declare the variables to output more frequently (every 30 mins). Make sure there are no spaces in the text file.

   
   

   +:h:24:RAINC,RAINNC,T2,Q2
   

   
   
   
   

   The above code indicates the following:

   \(+\)	add variables
   h:24	history stream 24
   RAINC, etc.	the variables to add to the new file

   
   

   Note

   Nested domains require a myoutfields_d0* file for each domain. The file can be named anything you choose, as long as its extension is .txt.

   
   
   
   
   
   

3. There is no need to run real.exe again; just wrf.exe. If successful, in addition to the history and restart files, the following file is generated and includes the requested variables at 30-minute intervals.

   auxhist24_d01_2019-11-25_12:00:00

   
   
   
   

4. If interested, use ‘ncview’ to visualize the variables in auxhist24_d01_2019-11-25_12:00:00.

Output Additional Variables

Use the “Runtime I/O” option to output additional variables to the history file (wrfout*). For e.g., to determine the amount of temperature change is results from radiation, PBL, cumulus and microphysics, add the following variables:

• RTHCUTEN : Theta tendency calculated by the cumulus scheme

• RTHBLTEN : Theta tendency calculated by PBL parameterization

• RTHRATEN : Theta tendency calculated by the radiation scheme

• H_DIABATIC : Latent heating from microphysics

Note

Alternative to using the Runtime I/O option, the same can be accomplished by adding an h to the I/O column for each variable in the Registry.EM_COMMON file, but that requires a full clean and recompile of the code, which can be time consuming.

1. Edit namelist.input. Start with the namelist set up for the Single Domain Run.

   &time_control
   restart_interval = 72000
   iofields_filename = "myoutfields_d01.txt",
   ignore_iofields_warning = .true.,
   
   &domains
   max_dom = 1
   

   
   

   Note

   These namelist settings intruct wrf.exe to read a file called myoutfields_d01.txt, and to either remove or add variables. ignore_iofields_warning=.true. allows the run to continue with only a warning message printed to the log file. If .false., the program aborts if .txt file contains errors. Set restart_interval to a large value to avoid writing a restart file - while outputting a restart file is good practice in the real world, it is unnecessary for this class.

   
   
   
   

2. Modify myoutfields_d01.txt - delete all its contents, then declare the new output variables and save the file. Make sure there are no spaces in the text file.

   +:h:0:RTHCUTEN,RTHBLTEN,RTHRATEN,H_DIABATIC
   

   
   

   This line of code indicates the following:

   \(+\)	add variables
   h:0	history stream 0, which is the standard wrfout stream
   RTHCUTEN, etc.	the variables to add to the history

   
   

3. There is no need to run real.exe again; just wrf.exe. If successful, the new variables should be included in the history output (wrfout*). Use ncdump -h <file-name> to list the contents of one of the history files, and/or visualize the variables using the “ncview” option.

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