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CROCO blowing up at 500m resolution

Hello, I am facing a problem with my CROCO setup, I was hoping if anyone familiar with this problem might have a possible solution. I am trying to simulate an idealized problem of an island within the open ocean. The island is elliptical shaped, as shown here in green landmask: image description

The min depth is 10 m, and steeps down to 1500 m towards the open ocean. The grid details are given below.

  • Horizontal resolution: 500 m
  • Min depth 10 m, max depth 1500 m
  • Haidvogel number: 0.203, Haney number: 2.96
  • theta_s = 5, theta_b = 0.0, Tcline = 10.0 Based on what I've read, the Haidvogel no should be < 0.25 and Haney no should be < 3.0, in order to give stable results. I initialized it with climatology from HYCOM 2018 and forcing from ECMWF.

I started with a time step dt of 10 sec and NDTFAST 120, but it is blowing up within 5 steps. Then I reduced the time step to 2 sec keeping NDTFAST the same, but it is still blowing up after 66 sec. Here is a timelapse video showing the zonal velocity transect and the SSH at each timestep till it blows up: video timelapse attached

I noticed that around the 54th time step, the velocity forms zig-zag patterns near the landmask. These patterns amplify to unrealistically large values. Also the SSH forms such patterns in the same area, and blows up eventually.

I further reduced the time step to 1 sec and it seems to run fine without blowup (1 sec timelapse). But running the model at such small time steps is quite unrealistic, so I am wondering what am I doing wrong here?

Here is a list of preprocessors I am using for my setup: TIDES OBC_EAST OBC_WEST OBC_NORTH OBC_SOUTH CURVGRID SPHERICAL MASKING WET_DRY NEW_S_COORD SOLVE3D UV_COR UV_ADV SALINITY NONLIN_EOS UV_HADV_UP3 UV_VIS2 UV_VIS_SMAGO UV_VADV_SPLINES TS_HADV_RSUP3 TS_DIF4 TS_VADV_AKIMA SPONGE GLS_MIXING GLS_KEPSILON CANUTO_A QCORRECTION SFLX_CORR CLIMATOLOGY ZCLIMATOLOGY M2CLIMATOLOGY M3CLIMATOLOGY TCLIMATOLOGY ZNUDGING M2NUDGING M3NUDGING TNUDGING ANA_BSFLUX ANA_BTFLUX SSH_TIDES UV_TIDES POT_TIDES TIDERAMP OBC_M2CHARACT OBC_M3ORLANSKI OBC_TORLANSKI SPLIT_EOS TS_HADV_C4 MPI_COMM_WORLD M2FILTER_POWER HZR VAR_RHO_2D UV_MIX_S VIS_COEF_3D DIF_COEF_3D TS_MIX_ISO TS_MIX_IMP TS_MIX_ISO_FILT NTRA_T3DMIX SPONGE_GRID SPONGE_DIF2 SPONGE_VIS2 NF_CLOBBER

Thanks, Sonaljit.