Sea ice velocity does not converge? -- Truncated too many times

[zi-hua-liu]

I am running the regional MOM6 model in MOM6-SIS2 coupled mode. However, the model has encountered two fatal errors that halted its execution. I have provided details of my model setup here in case it aids in diagnosing the issue.

• The model crashed with an error message indicating 'Sea ice velocity has been truncated too many times' (can seen from 'mom6_***.err' file). I am uncertain whether this error stems from any misconfigured parameters in my SIS_input or MOM_input setup. These parameters are consistent with those used in our global MOM6 model, which runs without any issues. ---- Just noticed that this issue might come from my boundary conditions, where input data in two boundaries (with numbers 002, 004) are wrong (constant values everywhere).
• In the MOM_override file, if the setup related to "tideamp" is activated, the model crashes during the initialization stage. I suspect that there might be an issue with the data type or format of the "tideamp" input, but I am not sure about the specific problem. Are there any template files available that address the input data for "tideamp"?

Any comments are appreciated! Thanks!

[theresa-morrison]

The truncation error is from the sea-ice velocity exceeding the limit set by the CFL criterion. If you regional model has a higher resolution than your global model you may need to decrease your time steps in the ocean and sea-ice model to maintain stability. But it sounds like you may have figured out the source of the of the incorrect velocities! I recommend testing your domain without OBC's when you are first setting it up.

For the tidal amplitude, I think you need to change the name of the variable in your tideamp_regional_nep.nc file to just "tideamp" rather than "tideamp_interp". I don't think the code allows you to specify the name of that field.

[theresa-morrison]

That error makes me think the error might be with the file name you are giving.
You are updating your MOM_override file to have:

#override INT_TIDE_DISSIPATION = True 
#override READ_TIDEAMP = True
#override TIDEAMP_FILE = "tideamp_regional_nep.nc"

when using this option, correct?

[zi-hua-liu]

Yes, that is correct. I updated my MOM_override with those above three functions to include 'tideamp'.

[zi-hua-liu]

May I ask for an 'tideamp' data example from OM4_025 or Arctic 12km cases? I have tried to set x/y to 1D instead of using 2D lon/lat, but it still does not work, with the same error... So I was thinking to reset my 'tideamp' data to be the same type as in the examples as you mentioned.

[yichengt900]

Hi @zi-hua-liu,

After reviewing your configuration, I believe the issue you encountered is due to the absence of H2_FILE (Variance of sub-grid scale topography) in your model configuration. This information can be found in the original global INPUT ocean_topog.nc. Below is an example script that can be used to regrid H2 data:

import numpy as np
import xarray
import xesmf

import sys

#First load regional grid
hgrid = xarray.open_dataset('ocean_geometry.nc')

mom_grid = {
    'lon': hgrid.lonh,
    'lat': hgrid.lath,
}


tide = xarray.open_dataset(
    '/collab1/data_untrusted/Xiao.Liu/Iron_Project/WHOI_NEP/INPUT/INPUT/tidal_amplitude_TPXO9_OM4p125.v20200922.nc',
)

h2 = xarray.open_dataset(
    '/collab1/data_untrusted/Xiao.Liu/Iron_Project/WHOI_NEP/INPUT/INPUT/ocean_topog.nc',
)

tide['h2'] = h2['h2']

tide_grid = {
    'lon': tide.lon,
    'lat': tide.lat,
}

tide_to_mom = xesmf.Regridder(tide_grid, mom_grid, method='bilinear', reuse_weights=False)
regridded = tide_to_mom(tide)

print(regridded)

# Rename variables
ds = regridded.rename_vars({'lath': 'ny', 'lonh': 'nx'})

ds.to_netcdf(
    './tideamp.nc', format='netcdf4' 
)

You also have to add the following lines in your MOM_override:

#override INT_TIDE_DISSIPATION = True 
#override READ_TIDEAMP = True
#override TIDEAMP_FILE = "tideamp.nc"
#override TIDEAMP_VARNAME = "tideamp"
#override H2_FILE = "tideamp.nc"

Keep in mind we normally simulate tide explicitly in regional application (e.g. OBC_TIDE_CONSTITUENTS = "M2,S2,N2,K2,K1,O1,P1,Q1,MM,MF").

[zi-hua-liu]

Thank you very much! It works after adding H2 data.

Later on, I may explicitly simulate tides in the regional model to compare the differences with the existing vertical tidal mixing parameterization. I appreciate your suggestions.