ROMS Granular model result in all variables

[kilarth]

Dear ROMS users,

I had an issue with all the variables, like temperature, that has in all levels in the vertical a granular aspect (attached figures). I still can figured out how to fix this.

I run ROMS 3.7 for 15 years simulation. Am using HYCOM initial conditions and climatology for each month. Forcing from COADS (heat, wind stress, sss, sst and fresh water). My open boundaries Che for free surface, Shc for 2D, RadNud for 3D and tracers, Rad for TKE.

Thanks

Jorge Ibarra

[jcwarner]

does it start out like that or evolve to that? check the fields in your grid file like dmde dndx. check angle.
are you using N2S2_HORAVG?

-j

[kilarth]

Hello,

Thank you for the reply. The first time steps looks smooth, and it evolve to the figure i attached.
I not used N2S2_HORAVG. Do you recomend to use it?

I'm doing some test and founded that using advection schemes for tracers TS_U3HADVECTION with TS_C4VADVECTION and for momentum UV_U3HADVECTION and UV_C4VADVECTION, i got better results.

Cheers

Jorge Ibarra

[jcwarner]

yes and try
#define N2S2_HORAVG

[kilarth]

Hello,

With respect to the variables dmde, dndx and the angle, i attached the figures.

I will activate N2S2_HORAVG and will report it as soon as possible.

Cheers

Jorge Ibarra

[arango]

I guess that the more fundamental question is what type of horizontal advection are you using? Are you specifying explicit diffusion and viscosity? What do you specify for vertical diffusion/viscosity parameterization closure? You should compute your Reynolds Number (U dx/nu), where U is the maximum velocity magnitude for your application. dx is grid spacing, and nu is diffusion/viscosity coefficient.

[kilarth]

Hello,

I used 4th order centered advection for tracers and momentum. For explicit viscosity TS_DIF4=2 and UV_VIS2=15. For the vertical parametrization closure: Mellor & Yamada, with Kantha and Clayson stability function, also to mention I added RI_SPLINES.

About the Reynolds Number from the log file, where U = 1.9 m/s, dx = 7000 m and nu = 15 m2/s; Re = 886.

Cheers.

Jorge Ibarra

[arango]

Well, that's your problem. You are using biharmonic diffusivity (m4/s), which scales as 1/12 * ABS(U) * (dx ** 3). A value for TS_DIF4 of 2 m4/s is too small You need values of the order of 2.0d+8 m4/s. That is, you are using a value that is eight orders of magnitude too small No wonder why your solution is so granular. I hope that you are not using MIX_S_TS, you will need, at least, mixing along geopotentials (MIX_GEO_TS) to avoid spurious diapycnal diffusion.

[kilarth]

Hello,

Thank you for the reply. Will do my new tests with that values.

Yes, I'm using MIX_GEO_TS.

Cheers

Jorge Ibarra