Modeling layered structure in deep Pacific circulation

The layered structure of the deep Pacific circulation is investigated using a multilevel numerical model with idealized geometry. The circulation is driven by sea surface heating and Newtonian body cooling at the southwest corner of the basin. The latter forcing is intended to incorporate thermohaline forcing in the Southern Ocean. A layered structure forms in the zonally averaged meridional circulation when the reference density for the body cooling varies vertically. The density balance between vertical advection and vertical diffusion holds in the zonally averaged field as well as in the interior. This balance, combined with the reference density for the body cooling, determines the zonally averaged vertical velocity and hence the zonally averaged meridional circulation from the zonally averaged continuity equation. This two‐dimensional mechanism for describing the layered structure for this three‐dimensional, rotating fluid model is identical to that for a two‐dimensional, nonrotating fluid model. The increased vertical structure is accompanied by the enhancement of some higher vertical modes, which brings about various changes in the three‐dimensional structure, such as the formation of a broad, diffusive, deep western boundary current.