Dynamics of the Atlantic meridional overturning circulation and Southern Ocean in an ocean model of intermediate complexity

A hierarchy of solutions is reported in which forcings and processes are individually introduced. The complete solution set includes a wide variety of solution types: with M>0 and M⩽0; with and without wind forcing; with, without, and for two parameterizations of northern-boundary sinking that represent cooling external to and within the North Atlantic; for a wide range of ν and τa; and for different closures. Novel aspects of the model and solutions include the following: use of VLOM, which allows Q forcing to be introduced realistically; the aforementioned closure, which allows V∗ to be determined when layer 1 represents both the surface mixed layer (h=hm) and the depth of subsurface isopycnals (h>hm); latitude y′, where layer 1 outcrops in the Southern Ocean, being internally determined rather than externally specified; and a boundary layer, based on Gill's (1968) solution, that smoothly connects the Southern- and Atlantic-Ocean responses across the latitude of the southern tip of South America. Finally, some solutions in the set are comparable to solutions to idealized, ocean general circulation models (OGCMs); in these cases, our solutions provide insight into the underlying dynamics of the OGCM solutions, for example, pointing toward processes that may be involved in eddy saturation and compensation.