numerical instability and CFL violation

[seashellingolds]

Hi all,

I am running a high-resolution model and having a problem with numerical instability. Attached figure shows the zonal velocity. Strong oscillation appears after several time steps and the magnitude soars into the sky. When reducing the DT, it goes several steps further. It seems an issue of CFL condition violation. The initial fields look smooth and reasonable. The horizontal scheme is 3rd upstream.

Is there any other workaround besides reducing the DT? The DT is already too small.

Thanks a lot!

[flcastej]

Hi Yisen,

¿Have you tried to use a different vertical sigma coordinates distribution? Sometimes playing with theta_s,theta_b... could be really useful. Here is some information:

https://www.myroms.org/wiki/Vertical_S-coordinate

Also, it could help you to check if you get a better stability using different turbulence schemes: GLS_MIXING, BVF_MIXING, MY25_MIXING, LMD_MIXING.In hte wikiroms webpage there are some information about them.
https://www.myroms.org/wiki/Vertical_Mi ... erizations

I have been working with HR models and playing with sigma coordinates and turbulence schemes have been really useful for me.

Good luck!!!