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Grid Boundaries


The east/west boundaries are periodic, and the north/south boundaries are solid walls, with a sponge layer from tex2html_wrap_inline1764 S to tex2html_wrap_inline1756 S, and tex2html_wrap_inline1764 N to tex2html_wrap_inline1756 N. At latitudes higher than tex2html_wrap_inline1764 (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 ( tex2html_wrap_inline1990 ) at latitudes higher than tex2html_wrap_inline1764 . The functional descriptions of the sponge layer are set in subroutine parinit.

Sponge layer functions spngh1 and spngh3 are defined as:



where tex2html_wrap_inline1994 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 tex2html_wrap_inline2000 and tex2html_wrap_inline2002 , respectively.

Note that though the east/west boundaries are periodic, numerically this is implemented without the use of ghostpoints.

next up previous contents
Next: Spherical Geometry Up: Model Code and Numerics Previous: Model Code and Numerics

Johnny Wei-Bing Lin
Wed Aug 26 16:58:31 PDT 1998