Unrealistic rain

Topics related to current and future physics in the WRF as well as any problems you may have.

Re: Unrealistic rain

Postby jimmyc » Sun Aug 24, 2008 11:49 pm

There isnt too much to try. You will need to dig into the data, analyze the soundings around these grid points to determine why the grid point storms developed.

ARW and NMM are dynamically different. The initialization techniques are different. The grid is different.
If there are options for w_damp, and decreasing the physics time step then I would do that. Also check the terrain including the land surface fluxes. That is not guaranteed to work, however. This may just be some numerical artifact given the state of the atmosphere.
The views expressed in this message do not necessarily reflect those of NOAA or the National Weather Service or the University of Oklahoma.
James Correia, Jr
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Re: Unrealistic rain

Postby PBLer » Mon Aug 25, 2008 1:58 pm

We've seen grid point problems like this over regions of steep topography, so you may need to perform some additional smoothing to the terrain field. Although, if that is the problem, its strange that the ARW wouldn't have the same issue. Its unfortunate that terrain smoothing seems to be the only solution to this problem but I have seen it take care of these bullseye problems many times...

There is a good chance that a future version of WPS/geogrid will perform the initial terrain smoothing, then check for potential trouble spots (large terrain slopes) and then do additional smoothing only to those grid points where the terrain slope exceeds a given threshold. That would be a nice option because I don't like smoothing more than necessary.

good luck
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Re: Unrealistic rain

Postby MeteoAdriatic » Tue Aug 26, 2008 3:55 am

Thx jimmyc and PBLer,

for now I can say just that this patterns occur only near slope terrain, so this explanation makes sense to me. Yes, strange that ARW does not show any similar symptom because it share same terrain data. As I see from Francesco's images, he also has problems ONLY near slope terrain patterns...
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Re: Unrealistic rain

Postby francesco.pasi » Fri Aug 29, 2008 6:19 am

Hi all
I have some good news. I have been discussing with Matthew Phyle, I want to really thank him, that suggested me some change in the NMM code that are very effective.
1) The most effective: apply some averaging of the vertical motion within the vertical advection
in dyn_nmm/module_ADVECTION.F at about line 1030 of the routine and in the subroutine VAD2, change




By setting TRADITIONAL to false, a horizontally averaged vertical motion is used to advect humidity and cloud water in the vertical.
This change will slow down the precipitation process and make localized storms less intense (but generally doesn't eliminate them completely.
2) Apply some horizontal diffusion.
In dyn_nmm/module_DIFFUSION_NMM.F
you can try to modify line 134
SLOPHC=SLOPHT*SQRT(2.)*0.5*18 (double the original value)
or even

SLOPHC defines a maximum allowable slope to the model surface for which lateral diffusion is permitted
By setting to a value (first case) allows diffusivity to be applied at more points in the horizontal
By setting to 99999. will ensure that lateral diffusion is applied everywhere (In my opinion too much)

3) Always in nmm/module_DIFFUSION_NMM.F
you might want to try to allow for some weak background diffusion in points where the topographic slope would generally lead to a complete zeroing of the impact of horizontal diffusion.
There are two blocks within dyn_nmm/module_DIFFUSION_NMM.F

SNE(I,J)=0. ! ->> change to SNE(I,J)=0.1 ??

and shortly below in the code:

SSE(I,J)=0. ! -->> change to SSE(I,J)=0.1 ??

You should try which is best for you
Of course you have to recompile and use new executable.
We are using these changes operationally (http://www.lamma.rete.toscana.it/wrf-web/index.html) with KF and in this period are performing very well
I don't know about winter time
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how can i increasing sensitivity of rain in WRF

Postby fard792 » Tue Apr 13, 2010 2:46 pm

hi all
can you tell me that how can i increasing sensitivity of rain (precipitation) in WRF ,
which schemes is good and which parameters must be change in namelist.input ?

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Re: Unrealistic rain

Postby alainaketh » Tue Oct 04, 2016 1:48 pm

Replying to fard792:

It's not about rain sensitivity, it's about how well the model can simulate the rainfall for a given event. There a a lot of things than influence the results: the dataset to run the model, the parameterisations used, domain configuration, etc. so you have to test all this variables to know which one(s) describe best your event.

That said, take a look at the recommendations about nesting:
http://www2.mmm.ucar.edu/wrf/users/tuto ... 1/nest.pdf

And read as much papers as you can about the schemes used, what type of event they're simulating, time span, etc. Use your own criterion as well and you'll come up with the potential configurations.

The most common parameters to be modified in the namelist.input file are in the &physics section
mp_physics: microphysics,
ra_lw_physics: longwave radiation (outgoing)
ra_sw_physics: shortwave radiation (incoming)
sf_sfclay_physics: surface layer
sf_surface_physics: land surface
bl_pbl_physics: Planetary boundary layer
cu_physics: cumulus

And the options available for each one can be found at http://www2.mmm.ucar.edu/wrf/users/docs ... 5.htm#Phys


Hydrology Researcher, University of Bristol
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