6x dx grid-scale noise with MYNN.

[wallis]

I have terrible grid-scale noise formations on PBLH, peak to peak is ~6x dx. dx is 2.7km.

I was using YSU PBL and there was a little bit of noise, I changed to MYNN PBL and sfclay and it is now even noisier. I would like to use MYNN.

MYNN configured like:
bl_mynn_tkeadvect = .false.,
bl_mynn_cloudpdf = 2,
bl_mynn_edmf = 1,
bl_mynn_edmf_mom = 0,
bl_mynn_edmf_tke = 0,
bl_mynn_mixlength = 2,
scalar_pblmix = 1,

What causes this?

Why is it not filtered out with diff_6th_opt?
diff_opt = 1,
km_opt = 4,
diff_6th_opt = 2, 2, 2,
diff_6th_factor = 0.20, 0.20, 0.20,
diff_6th_thresh = 0.1, 0.1, 0.1,
diff_6th_slopeopt = 1, 1, 1,

 

[Ming Chen]

Please set diff_6th_factor = 1, 1, 1, then try again. Let me know whether this is helpful.

 

[wallis]

I tried with higher values, above 0.5 I get immediate CFL violations

 

[Ming Chen]

If you reduce time_step, turn on w_damping, and specify a higher value of epssm, can you get rid of the CFL issue?