Cyclonic rings formed by the Gulf Stream 1965-66

Abstract

A cyclonic ring of Gulf Stream origin is defined to be a member of a special class of eddy; when the meandering Gulf Stream forms a long loop to the right of its downstream direction and the two sides of the loop, with currents flowing in opposite directions, approach each other and come in contact, a ring is formed consisting of a closed segment of the Stream revolving cyclonically around a mass of cold water detached from its former position in the slope water area to the left of the Stream. The first observations of the formation, migration and decay of such rings on seven cruises, covering the period from September, 1965, through February, 1966, are described. The two rings observed started as elliptical shapes, the long axis about 250 km, and gradually changed to circles about 110 km in diameter. The maximum surface currents, on the order of 150 cm/sec, continued strong over the five month period. The rings migrated at a rate of about 10 cm/sec, following irregular, probably anticyclonic paths with a net displacement to the SW. It is estimated that they have a life span of about 12 months. On the bases of a few crude assumptions, using average annual surface current speeds, the monthly net departure of the Gulf Stream from its mean position and a few transport values, it is estimated that from 5 to 8 cyclonic rings form per year.