The east/west boundaries are periodic, and the
north/south boundaries are solid walls, with a sponge
layer from 
S to 
S, and N to
N.
At the north-south boundaries, meridional velocity v
is set to zero. Thus, at the northern boundary, both v0(i,NY)
and v1(i,NY) are set to zero. To describe the southern boundary, an
extra point has been added at the southern-most extent of
arrays v0 and v1. Thus, the y direction of
these two arrays (and arrays which depend on them, such as
psi0) are actually dimensioned 0:NY instead of 1:NY, as
the other arrays (such as u0 and u1) are.
Then, this southern-most point
of both v0 and v1 are set to zero.
Note that though the east/west boundaries are periodic, numerically this is implemented without the use of ghostpoints.