Analysis Nudging - Spectral and 3D

In this example we are going to use the same standard case data as before. If you no longer have the original met_em.d01.* files from this case, please return to the Single Domain case and generate them again.

We are going to use 3D spectral nudging. (**Note, surface nudging cannot be used with spectral nudging, only with grid nudging).
 

Basic setup

Make sure you are in the WRFV3/test/em_real directory.
Link in the met_em* files

ln -sf ../../../WPS/met_em.d01.* .

 

Analysis Nudging Specifics

• To run the model with analysis nudging, you need to add the &fdda section to your namelist.
  You can also find an example of this section in the file WRFV3/test/em_real/examples.namelist
  (Hint: cutting and pasting the required namelist section from this file will be easier than typing-in the new section)
   
  Also set max_dom = 1 for this run.
   
• We are only activating 3D analysis nudging, and we are going to use spectral nudging (grid_fdda=2).
  We are nudging domain 1, and for waves longer than 1000km (wavenum 2 for a 30km domain, with 70 grid points works out to about 1000km).
  Add the following in the following lines in the &fdda section of your namelist.input file
  
      grid_fdda = 2, 0,
      gfdda_inname = "wrffdda_d<domain>",
      gfdda_interval_m = 360, 360,
      gfdda_end_h = 24, 24,
      io_form_gfdda = 2,
      fgdt = 0, 0,
      fgdtzero = 0, 0,
      if_no_pbl_nudging_uv = 1, 1,
      if_no_pbl_nudging_t = 1, 1,
      if_no_pbl_nudging_ph = 1, 1,
      guv = 0.0003, 0.0003,
      gt = 0.0003, 0.0003,
      gph = 0.0003, 0.0003,
      xwavenum = 2, 2,
      ywavenum = 2, 2,
      if_ramping = 0
      dtramp_min = 60.0

 

• Run real.exe as before, and this will create a file called "wrffdda_d01", in addition to wrfinput_d01 and wrfbdy_d01 files.
   
• Run wrf.exe as  (save old wrfout files if you want to compare them to see the effect of nudging).

 

Check your output:

• Check to see what is printed to the log files.
  Look specifically for the extra output concerning nudging - you should see something like this:
    D01 Spectral nudging for wind is turned on and Guv= 0.3000E-03 xwave= 2 ywavenum= 2
    D01 Spectral nudging for temperature is turned on and Gt= 0.3000E-03 xwave= 2 ywavenum= 2
    D01 Spectral nudging for geopotential is turned on and Gph= 0.3000E-03 xwave= 2 ywavenum= 2
    D01 Spectral nudging for wind is turned off within the PBL.
    D01 Spectral nudging for temperature is turned off within the PBL.
    D01 Spectral nudging for geopotential is turned off within the PBL.
  
  
• Tail the log files and look for "SUCCESS COMPLETE WRF".
• Type the following to see output times available in wrf history file:
   
      ncdump -v Times wrfout_d01_
   
  
• Try the netcdf data browser 'ncview' to examine your wrf output file
• Generate graphics with one of the supplied packages.




Organization Suggestion:

Recall the suggestion (from the "basic" case) to create a directory to put your files in. Do this again for this case:

mkdir nudging

and then copy the necessary files into that directory to preserve them for potential later use.

You can now continue to run other practical examples.