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How to understand AFWA_VIS values

J

janac4

Member
Hello,
I have activated afwa_vis_opt both in a normal wrf run and a wrf-chem one (with dust_opt activated). In both cases visibility values are very large (values of 200000 m are achieved, see the picture attached and namelist.input file).
However in another simulation (vis-2.png, higher resolution, matches namelist-input-2.txt) values make more sense and I can't understand why. Is it only a geographical matter or something in the configuration of the model makes this large differences?
Which is the correct interpretation of AFWA_VIS values?
Thanks a lot.
 

Attachments

  • afwa-vis.png
    afwa-vis.png
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  • namelist-input.txt
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  • vis-2.png
    vis-2.png
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  • namelist-input-2.txt
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Hi,
First of all, apologies for the long delay in response. We've been busy with some other tasks and have gotten a bit behind in forum questions.

I can't say for sure, but I believe one primary reason you're seeing odd values using the first namelist is because of the very coarse resolution of 100 km. I think it's difficult for any parameterization and/or diagnostics to produce reasonable results with the resolution is that coarse. We typically recommend setting your domain to a resolution (dx/dy) ratio of about 3:1 or 5:1 between the resolution of the input data, vs. the resolution of your domain.
 
Hello again,
I have been working with 1 km models in a tropical region and used AFWA diagnostics activated to forecast visibility. However I still see very high values of this magnitude in both GFS and WRF model.
GFS seems to have an upper limit of 25 km, does it make sense? Does anyone know why?
WRF model forecasts visibility values up to 100 km, which is unreasonable. I can also see daily patterns of variability in WRF model, and would like to understand how it works.
Thanks a lot.
 
Hi,
I wasn't sure about this one, so I spoke to our physics expert who said they were pretty sure this is supposed to work with the AFWA dust scheme, otherwise only hydrometeors reduce visibility. Are you using the dust scheme?
 
Hello,
I have attached visibility contributions from hydrometeors (pink line) and surface haze (blue line). In this simulation I'm not using wrf-chem so I have no dust contribution. Final AFWA_VIS visibility is the minimum value of this lines, which in general result in values higher than 15 km.
 

Attachments

  • visibility.jpeg
    visibility.jpeg
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Hi,
I just want to let you know we haven't forgotten about you. I *think* I've narrowed down the issue in the code, but I need to confirm it with someone with more experience with this code first. I'll get back to you as soon as I hear anything. Thank you for your patience.
 
Hi,
I've talked this over with our physics experts and they claim that these visibility values can be realistic, especially with drier conditions. So I think it's okay for you to continue.
 
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