The Spectral Nudging Option¶

n this exercise you will using 3D spectral analysis nudging

Spectral Nudging

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).
See details about the different nudging options

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

Analysis Nudging Specifics¶

If you have the namelist saved from the Single Domain Run, copy that to the wrf/test/em_real directory:
```
cp single_domain/namelist.input .
```
To run the model with analysis nudging, add the following namelist parameters to the &fdda namelist record (you can see another example in wrf/test/em_real/examples.namelist). Cutting and pasting the required namelist section from this file will be easier than typing-in the new section. Also make sure max_dom=1.
```
&domains
max_dom = 1

&fdda
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).
Link in the met_em* files from wps.
Run real.exe as usual, which should create a file called wrffdda_d01, in addition to the wrfinput_d01 and wrfbdy_d01 files.
Run wrf.exe as usual (save old wrfout files if you want to compare them to see the effect of nudging).

See what is printed to the log files (rsl.out.*). Look specifically for extra output concerning nudging - something similar to 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.

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