Typically, at initial condition time, the model is at rest with a specified density distribution. This is accomplished by zeroing all velocities (internal and external mode) and setting potential temperature and salinity at each grid cell using one of the options described below. All passive tracers are initialized to unity in the first level (k=1) and zero for all other levels. In principle, initial conditions could also come from a particular MOM restart file although this is not the intent of the following options. One and only one of these options must be enabled.