Noise below the mixed layer when using AnisotropicMinimumDissipation

[jhdong2016]

Hi all, I am simulating an ocean surface mixed layer. However, I always get lots of noise in the ocean interior below the mixed layer. I have applied a Gaussian-mask sponge layer near the bottom. But the noise is still there. Below are two figures of the vertical velocity and buoyancy perturbations. Any suggestions?

Here are the codes for the sponge.

ps. the whole depth is Lz = 150 m and the mixed layer is about 80m.

######========================================
damping_rate = 1/1800 # relax fields on a 100 second time-scale
bottom_mask = GaussianMask{:z}(center=-grid.Lz, width=grid.Lz/3)
uvw_sponge = Relaxation(rate=damping_rate, mask=bottom_mask)

model = NonhydrostaticModel(; grid, coriolis,
advection = WENO(),
timestepper = :RungeKutta3,
tracers = :b,
buoyancy = BuoyancyTracer(),
closure = AnisotropicMinimumDissipation(),
stokes_drift = UniformStokesDrift(∂z_vˢ=∂z_vˢ),
boundary_conditions = (v=v_boundary_conditions, b=b_boundary_conditions),
forcing=(u=uvw_sponge, v=uvw_sponge, w=uvw_sponge))
#####============================================

[navidcy]

Hi @jhdong2016, thanks for your interest in Oceananigans!

Personally I find it very difficult to help out without something that I can run and reproduce your results. Could you post your script somewhere also for making the plots. Something I can copy/paste in the REPL or just write include("jhdong_script.jl")?

It's often useful to post the version of Oceananigans you are using (and the rest of dependencies). E.g., post the output of using Pkg; Pkg.status().

Do I understand correctly or is it my impression that you have depth in the horizontal axis?

[jhdong2016]

THanks for the reply. Here are the files that may help.

si_langmuir_case0.8m.jl.txt

[navidcy]

Thanks!

You seem to be using a very very old version of Oceananigans; v0.79.0 (from 2022).
Could you try to update to the latest version and see if the issue(s) remain?

[jhdong2016]

Thanks for the suggest! Let me update it and see if the issue is fixed.

[glwagner]

This is common to observe with AnisotropicMinimumDissipation. If you don't need the dissipation rate or eddy diffusivities explicitly, you could try using closure=nothing and advection=WENO(order=9) instead. This might solve your noise problem and also give you a higher effective resolution.

Can we convert this to a discussion? I don't think this is a bug in the code.

[glwagner]

@tomchor might have more to say

[glwagner]

And yes more generally it's best if you include your whole script so that the simulation can be reproduced. In particular here we need the grid, initial condition, and time step to fully grasp what's doing on.

[jhdong2016]

This is common to observe with AnisotropicMinimumDissipation. If you don't need the dissipation rate or eddy diffusivities explicitly, you could try using closure=nothing and advection=WENO(order=9) instead. This might solve your noise problem and also give you a higher effective resolution.

Can we convert this to a discussion? I don't think this is a bug in the code.

Please convert it into a discussion. And I am updating the version and will try your suggestion! Thanks!