For global models, it is often useful to plot the overturning streamfunction within particular basins in addition to the global ocean. With option merid_by_basin, the streamfunction can be computed for different ocean domains using masks set up by the researcher. See the code for details of how to set up the masks. Also note that MOM generically computes an ASCII file kmt.dta which is a useful place to start when constructing the masks. An objective way to construct masks is to use a ``fill algorithm'' such as that used in MOM for constructing the land-sea boundaries.