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Problem with wind and the change of vertical layers.


New member
Hello everyone,

Sorry for my English.

You'll see, I've run WRF with the default distribution of vertical layers (in my case, e_vert=35).
For a better resolution in the lower layers, I set up the following distribution:
eta_levels = 1.000, 0.998, 0.994, 0.990, 0.988,
0.982, 0.978, 0.972, 0.968, 0.958,
0.954, 0.942, 0.936, 0.922, 0.914,
0.898, 0.886, 0.868, 0.850, 0.830,
0.808, 0.782, 0.754, 0.722, 0.686,
0.648, 0.602, 0.554, 0.498, 0.436,
0.368, 0.290, 0.204, 0.108, 0.000.

However, with the same configuration in another case, I've encountered the error "segmentation fault" and problems with the "CFL". I resolved the error with "eppsm=0.9," "w_damping=1," and decreased the time step.

But, even though the values of 'temperature' at lower levels are now approaching what I am looking for, the wind speed and direction values worsen. I suspect it's because of 'eppsm' or 'w_damping,' but I would like to know if there is any way to correct these wind values, or to solve the 'segmentation fault' problem in another way.

Thanks in advance,
For CFL violation, we often suggest to decrease time step first. If a smaller time step cannot solve the issue, then we can turn on w_damping and try again. A larger epssm works effectively when the model domain is over large topography area such Tibet.

The issues related to wind sped and direction, can you clarify what errors have you seen in your case?
Hello Mr. Chen. Thanks for you response.

In my case, I'm running over the Andes.
The issue with wind is arise when plotting wind direction with the default distribution (the top rose plot) which appears to match the data better. However, with the manual distribution that focuses more on lower levels,I get the bottom rose plot. Although the differences between the rose plots are not critical, they do exist. I understand that this could be related to eppsm and w_damping. Do you recommend first decreasing the timestep, then increasing eppsm, and finally activating w_damping?

Surface wind simulation is greatly affected by local terrain. We are aware of WRF's insufficiency in surface wind simulation.

Yes you are right to first decreasing the timestep, then increasing eppsm, and finally activating w_damping to overcome the CFL violation.

You may also turn on the option "topo_wind" in namelist,.input (&physics). Please try both topo_wind = 1 and topo_wind =2, and see which option can give you better results. Note that this option can only work with YSU PBL scheme.

Hope this is helpful for you.