COMPARISON OF AUTONOMOUS LAGRANGIAN CIRCULATION EXPLORER AND FINE RESOLUTION ANTARCTIC MODEL RESULTS IN THE SOUTH-ATLANTIC

The motions of eight Autonomous Lagrangian Circulation Explorer (ALACE ) floats released near 750 m depth in Drake Passage and followed throu gh the South Atlantic are described and compared with emulations made by advecting model floats through 12 monthly snapshots of velocity fro m the fine resolution Antarctic model (FRAM). Both ALACEs and FRAM rep roduce the major features of the general circulation as follows: stron g intermediate depth how in Drake Passage, bifurcation of the Antarcti c Circumpolar Current (ACC) passing over the Falkland Plateau, a stron g Falkland Current, its confluence with the Brazil Current, and modera te zonal flow across the South Atlantic. FRAM versus ALACE comparisons are made in both the Eulerian frame and using observed and modeled tr ajectories. In Drake Passage, where float velocities agree with earlie r observations, FRAM velocities are about twice too big. Both FRAM and ALACE velocities are consistent with an O(100 Sv) Falkland Current. T n the central South Atlantic the few available float observations indi cate the ACC and South Atlantic Current (SAC) to be more localized tha n in the model. Eddy kinetic energy is much stronger in the observatio ns than in FRAM. Float dispersion in both the model and observations i s due primarily to mean shear. Initial RMS particle separation of 100 km grows to nearly 1000 km after 1 year, but most of this is associate d with floats that take different paths of the general circulation. Th e observations indicate that eddy effects are particularly important n ear the Falldand-Brazil Current confluence in allowing Antarctic Inter mediate Water to transfer from the ACC to the SAC, from which they may enter the subtropical gyre.