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Help with nudging (fdda)

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New member
Hi. I was wondering if I could get some help on how to set up a WRF run with nudging. According to the what I have been able to find in the WRF users' pages, I have added the following lines to my namelist.input to obtain nudging:
 grid_fdda                           = 1,
 gfdda_inname                        = "wrffdda_d01",
 gfdda_interval_m                    = 360,
 gfdda_end_h                         = 48,
 io_form_gfdda                       = 2,

REAL.exe works fine and generates the wrffdda_d01 file as expected. WRF.exe also runs, however, the results are exactly the same as without nudging. Differences between nudged and unnudged 9-day runs are equal to zero for all fields for all output times.

Inspection of the log files indicates that nudging is apparently happening (see below):

D01 3-D analysis nudging reads new data at time =      0.000 min.
D01 3-D analysis nudging bracketing times =     0.00  360.00 min.
D01 3-D analysis nudging reads new data at time =    360.000 min.
D01 3-D analysis nudging bracketing times =   360.00  720.00 min.

What am I doing wrong? My namelist is attached.

I also noticed that, despite setting "gfdda_end_h = 48", the wrffdda_d01 file covers the entire length of the run, which is 9 days. It seems like WRF is ignoring gfdda_end_h.

Any help will be much appreciated. Cheers


  • namelist.input
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I just run a test case using WRFV4.3. I also copy your &fdda section to my namelist.input. The fdda nudging option works just fine and I can see obvious impacts of grid nudging. Attached is the difference of wrfout with and without nudging after 36 hours f integration.
I also attach the names;list.input I used just in case you want to take a look. Would you please double check your results and et me know if you come up with some new information. Thanks.


  • namelist.input
    6.6 KB · Views: 103