Intergyre Communication in a Three-Layer Model

Abstract

A three-layer, wind-driven, general circulation model involving both subtropical and subpolar gyres has been developed to study intergyre exchange. Following some early studies, the present work allows flow to baroclinically cross the intergyre boundary. This model differs from past work by examining a three-layer fluid. Solutions with both southward and northward subsurface flows are obtained. The two principal objectives of this work are to clarify the structure and maintenance of the permanent thermocline and to aid in understanding the distribution of deep water masses. A class of thermocline structures at the zero Ekman pumping line has been constructed that permits intergyre exchange, or communication. The zones of exchange are called windows. In this study, the windows have several unique properties relative to those computed elsewhere, and exhibit relatively rich structure. Principally, the addition of an active third layer allows a new second baroclinic window to open. This new window is physically and dynamically distinct from the first window (found in previous studies), and most of the intergyre baroclinic transport can occur through it. Its appearance also supports the conjecture that the number of communication windows increases with the number of active layers. In addition to the model development, observed potential vorticity distributions have been reexamined within the context of this model. Possible explanations for deep potential vorticity contours in the North Atlantic and North Pacific oceans are proposed.