[MITgcm-support] Volume conservation with open boundaries and tides

[Ruan Xiaozhou]

Dear MITgcm users,

I have been constructing a nested model with OBCS, RBCS as well as tidal forcing. The model uses nonlinear free surface. I turned on USEobcsBALANCE = .TRUE. and have set OBCS_balanceFacN/S/W/E all to 1 but when I plotted the domain averaged ETA as a time series, I see a big oscillation with 1-2m’s amplitude. This means I’m gaining/losing mass in the model domain. I was wondering if my settings above only correct the velocity OBCS to have zero net flow rather than the total velocities including the tidal flows? Is there anything I’m missing here in the setup to conserve volume in the model? Thank you so much for your help.

Best,
Xiaozhou