Previously, I posted a couple of discussion threads on 'unrealistic' velocities forming along the bathymetry on my domain. As a follow-up - I did some more analysis, and found out that the unrealistic velocities are forming due to

**spurious patterns in the pressure gradient, evolving along the spatially varying bathymetry**. Below, are a few plots showing the problem.

Pressure gradient at the 1st time step Notice the small-scale patterns forming. This is happening along the varying bathymetry. (plot below) Velocity difference between 1st and 2nd timesteps The anomalies in the velocity, match with the pressure gradient.

In this run, the pressure gradient is calculated with standard density jacobian algorithm. I was going through some threads, where it is said that the pressure gradient on a sigma coordinates can form errors, giving rise to spurious currents (probably that's what is happening here).

Any suggestions on how to accurately estimate the pressure gradient? I tried smoothing the bathymetry, but that doesn't solve the problem. Strong gradients eventually form at later times, shooting up the velocity to unrealistic levels.

Thanks,

Sonaljit.