On the eddy field in the Agulhas Retroflection, with some global considerations

Abstract

Moored instrument data are used to describe and summarize selected characteristics of the observed time‐dependent flow at low frequencies, that is, the eddy field, in the Agulhas Retroflection. In addition, the basic features of the eddy kinetic energy (KE) distributions in the Agulhas Current System (ACS) are compared with those from analogous strong current regimes in other oceans, concentrating on those from the Gulf Stream System (GSS). Similarities between the eddy field in the ACS and the GSS are found to include the vertical structure of KE as well as its distribution with frequency. This correspondence between the eddy fields in the ACS and GSS is probably associated with a consonant physical mechanism (mixed barotropic/baroclinic instability) for eddy generation in the presence of comparable upper and intermediate layer mean flow characteristics. It is also pointed out (for the first time to my knowledge) that the upper 1000 m or so (σθ ≤ 27.4) of the ACS and GSS can have a very similar distribution of transport in potential density classes. Relationships between the eddy field and the general circulation for the ACS and GSS with the Kuroshio Current System and the North Brazil Current System are described in less detail and scope. It seems probable that the characteristics of the global eddy field are strongly affected by the interbasin‐scale upper and intermediate layer replacement flows associated with the global thermohaline circulation.