Analysis Nudging - Spectral and 3D

In this exercise you will be using 3D spectral analysis nudging, which is an upper-air nudging option and selectively nudges coarser scales only. This option also nudges geopotential height.

Note Surface nudging cannot be used with spectral nudging (it can only be used with grid nudging).

Analysis Nudging Specifics

You will use the Single Domain case again. If you no longer have the original met_em.d01.* files from that case, please return to the Single Domain case and generate them again.

1. To run the model with analysis nudging, you need to add the following namelist parameters to the "&fdda" namelist record (you can also find an example in wrf/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.

       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

   Note You are only activating 3D analysis nudging, and are using spectral nudging (grid_fdda=2). You are nudging domain 1, for waves longer than 1000km (wavenum 2 for a 30km domain, with 70 grid points works out to about 1000km).

   
   
   


2. Also set "max_dom = 1" for this run.



3. Run real.exe as before, and this will create a file called "wrffdda_d01", in addition to the wrfinput_d01 and wrfbdy_d01 files.



4. Run wrf.exe as before (save old wrfout files if you want to compare them to see the effect of nudging).



5. Check to see what is printed to the log files (rsl.out.*). Look specifically for 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.
   
   

Continue to More Exercises If you plan to attempt more exercises right now, you can access the cases studies menu by clicking here.