[Wrf-users] Damping and Diffusion Issues

Huber, David dbh409 at ku.edu
Thu Oct 21 08:15:40 MDT 2010

Hello All,

I am having an issue with vertical velocities at 700mb on a 12km grid spacing model run for July 2001. The full simulation is for June-July 2001, but the issue is most noticeable in July. The first time I ran the model, I opted not to use damping or 6th-order diffusion, which resulted in the following month-long average 700mb w-field:
The grid scale noise over N Texas was concerning to me, so to remove 2dx noise I turned on 6th order diffusion (diff_6th_opt = 1, diff_6th_factor = 0.12) and in case the problem was being caused by the interaction with the mountain range in eastern New Mexico and the subtropical high positioned over N Texas, I also turned on w-Rayleigh damping (damp_opt = 3, damp_coef = 0.2). This resulted in the following w-field at 700mb:

(units in both images are cm/s)

This solution removes the grid scale noise, but introduces a wave-like solution everywhere. Also, it introduces positive vertical velocities over the southeastern corner of the domain (you'll have to click on the links to see this, since the pictures are too large to show on this forum). I am leaning towards the second solution, but I worry about whether the wave-like velocities should be noticeable on a month-long average. I'm really at a loss as to how to proceed. Should I consider different options for damping and diffusion? Is the grid scale noise OK, or if not, does the damped and diffused solution seem OK? Any incites would be much appreciated.



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