Comparison of Methods of Estimating Mean Synoptic Current Structure in "Stream Coordinates" Reference Frames: Impact on Structure, Transport and Dynamical Inferences With an Example From The Antarctic Circumpolar Current

Douglas S. Luther, Univ. of Hawaii at Manoa, Honolulu, Hawaii
Christopher S. Meinen, Univ. of Hawaii at Manoa, Honolulu, Hawaii


Stream coordinates techniques, that is, the methods of deriving the mean "synoptic" structures of narrow meandering ocean currents, have been in use for nearly two decades and have resulted in improvements in our understanding of the dynamics and transports of such currents. Stream coordinates have been applied to a wide range of currents, including the Gulf Stream, North Atlantic Current, Kuroshio, and Antarctic Circumpolar Current (ACC). Studies of these currents have involved different types of measurements, and have employed somewhat different assumptions to convert Eulerian measurements into a stream-coordinates reference frame. The key issues are how to determine, at any particular time, the location and direction of the core of the meandering jet relative to observations taken at fixed geographical locations. A recent experiment in the ACC's Sub-Antarctic Front (SAF) southwest of Tasmania, involving overlapping arrays of current meter moorings, inverted echo sounders, and horizontal electric field recorders, has provided an opportunity to test various stream coordinates methods to determine how well they achieve the goal of producing an accurate mean "synoptic" picture of the SAF current. It is found that, at least for the SAF southwest of Tasmania, the common assumption of a meandering "frozen field" baroclinic structure leads to the concealment of real baroclinic divergence and to an incorrect broadening of the current and temperature structures. The impact of the differing stream coordinate structures on dynamical inferences and transport estimates will be discussed.