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
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
spngh3 are active;
sponge layer terms
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
Sponge layer functions
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
T) variables are located.
At the north-south boundaries, meridional velocity v
is set to zero. Thus, at the northern boundary, both
v1(i,NY) are set to zero. To describe the southern boundary, an
extra point has been added at the southern-most extent of
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
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
v1(i,0)) are set to zero. As a
and , respectively.
Note that though the east/west boundaries are periodic, numerically this is implemented without the use of ghostpoints.