Can anybody comment on why boundary conditions are implemented for tracers in pre_step3d.F?
To my understanding, pre_step3d initializes time stepping of interior variables, u(:,:,:,nnew), v(:,:,:,nnew), and t(:,:,:,nnew,:).
Then, why lateral boundary conditions are implemented for the intermediate tracer t(:,:,:,3,:) at the very end of pre_step? In the same sub, boundary conditions are not implemented for u and v.