22.8.5 Sponge boundaries

If option sponges is enabled, a Newtonian damping term is added to the tracer equation through the source term near northern and southern boundaries where $\gamma^{-1}$ is a Newtonian damping time scale input through a namelist and $t^\star_{i,k,j,n}$ is interpolated in time from data prepared by the scripts in PREP_DATA. If option equatorial_sponge is enabled, then the profile from Equation (28.1) is used for $t^\star_{i,k,j,n}$ instead of data prepared in PREP_DATA. Refer to Section 14.4 for information on namelist variables. The time interpolation method is the same as described in Section 19.2.

$$source_{i,k,j} = source_{i,k,j} - \gamma\cdot (t_{i,k,j,n,\tau-1} - t^\star_{i,k,j,n})$$ (22.57)