How to make the 3D seamount test have smaller velocities?

[claireyung]

The seamount plots have relatively big velocities. Velocities for the seamount topo are 10^(-4)m/s and bigger than the ice shelf, as shown in Pedro's plot:

Why is this? How can we reduce them?

Some examples of achieving lower velocities and thoughts:

The MOM6 seamount tests (2D, with a high viscosity of KH=1000 and comparatively low resolution) have velocities 10^(-12)m/s.

The ISOMIP+ topography in zstar coordinates can reach down to 10^(-11)m/s as discussed in this forum post .

Problem parameters I found that cause the no-ice-shelf-but-3D-topo-zstar to have growing velocities were (also in above post):

#override DRAG_BG_VEL = 0.05 ! Default is 0.00
#override KH = 6.0 ! ISOMIP Asay-Davis protocol, original is 0
#override MIN_THICKNESS = 0.001 ! Original is 1E-12
#override MASS_WEIGHT_IN_PRESSURE_GRADIENT = False ! Original = True

comparing with the current MOM_input, we have KH = 1000, MASS_WEIGHT_IN_PRESSURE_GRADIENT = True, DRAG_BG_VEL = 0.05, MIN_THICKNESS = 1.0E-03. Perhaps the mass_weight_in_pressure_gradient parameter??

[pedrocol]

Thanks for this Claire, I think we should use viscosity values that are used in normal realistic runs, since the final end is to have acceptable spurious currents in realistic contexts. I do agree that we should keep investigating ways to reduce the spurious currents. One possibility is to mask the pressure gradient in those layers in the proximity to vanishing layers. I discussed this with Bob, he thinks that this may not be necessary, but still possible