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 latitudes higher than (this cutoff value
is set by the local variable y0 in subroutine parinit),
this sponge layer reduces heat and moisture flux, and increases momentum
damping, with a linear drop-off. This layer is used to reduced excessive
boundary precipitation. The code contains options for damping out other
dynamical and physical components in this sponge layer. However, in the
standard release, only spngh1 and spngh3 are active;
sponge layer terms spngh2 and spngh4 are commented
out. Respectively, these latter terms increase diffusion and reduce
precipitation ( 
) at latitudes higher than . The functional
descriptions of the sponge layer are set in subroutine parinit.
Sponge layer functions spngh1 and spngh3 are defined as:
where 
is the latitude (in degrees) at the jth grid point.
In Figure 2.1, this is the location where the u
(and T) variables are located.
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.
An exception is vort0, which one might think is
dimensioned 0:NY, but actually is dimensioned 1:NY.
Then, this southern-most point of both v0 and v1
(i.e. v0(i,0) and v1(i,0)) are set to zero. As a
reminder, v0(i,0) and v1(i,0) describe
and 
, respectively.
Note that though the east/west boundaries are periodic, numerically this is implemented without the use of ghostpoints.