Limited domain models must consider the manner for which open boundaries are handled. In general, the mathematical consistency of open boundaries is not clear, so much care should be exercised. In MOM, the methodology of Stevens (1990) has been implemented (Section 28.3.5).
An alternative to open boundaries is to restore fields along the boundary to some prescribed values. This method goes by the name of ``sponge'' boundary conditions. Details of the MOM implementation of sponges is described in Section 28.3.4.