Upstream control of Agulhas ring shedding

Abstract

Rings shed in the Agulhas retroflection region play an important role in the global thermohaline circulation. The sheding of these rings has been considered very irregular. In this paper, we present evidence for remote control of the timing and frequency of these events. This turns out to be a far more regular process, at a frequency of 4-5 cycles per year. The movement of the Agulhas retroflection, and thereby the shedding of rings, is timed by incomming eddies from the upstream regions. Eddies from the Mozambique Channel, and from the East Madagascar current reach the Retroflection region at the frequency of 4-5 times per year. The existence of these eddies can be related to incomming Rossby waves that cross the Indian ocean and reach the Agulhas current system. These may in turn be part of a basin wide oscillation. The irregularity found in ring shedding statistics can be ascribed to processes occuring between the actual shedding and the first unamigouos observation of a seperated ring.