Particle Pathways in the Gulf Stream

Abstract

An experiment is under way to study the kinematics, dynamics, and path evolution of the Gulf Stream front between Cape Hatteras and 60°W. The Rafos float, which can track the true motion of water parcels along density surfaces which slope steeply across the Gulf Stream, has recently been developed for this study. These instruments are launched in the center of the Gulf Stream every 5–15 days for a 30-day mission. Each float provides a trajectory and a continuous record of temperature and pressure along the trajectory. Our results so far show that: a) cross-stream motion has a significant vertical component (ranging to some 0.1 cm s−1) compared to vertical velocities in midocean; b) floats systematically shoal (upwell) as they approach anticyclonic meanders and deepen (downwell) as they approach cyclonic meanders; c) more than half of the floats launched so far remained trapped in the Gulf Stream for distances on the order of 1000 km; d) when floats do escape from the stream, it is more likely they will do so to the south; and e) both internal processes, such as the rapid growth of meanders, and external features, such as nearby rings or eddies, can expel or extract floats from the stream. These observations are also being used in numerical simulations of the Gulf Stream to develop predictive skills for the path of the current.