ORCA2 simulation produces noisy tracer fields

running some technical tests with ORCA2 and NEMO 4.0.6 we realized that after a few months tracer output fields become unrealistically noisy in the Tropics west off South America (see figure attached for 5-daily SST after ~1 year of simulation starting from rest). This occurs using the default namelist, and the 3D viscosity file provided. Increasing the viscosity in the Tropics fixes the issue, but I wonder if this is a well-known issue with the latest NEMO version or not, or due to other factors,


What you see is the signature of tropical instability waves to me (unless I am missing the point).

I agree with @clem: this does not look as an issue to me.