Tracking Three Meddies with SOFAR Floats

Abstract

Three Meddies were tracked for up to two years in the Canary Basin using neutrally buoyant SOFAR floats. These Meddies have cores of warm, salty Mediterranean Water and are approximately 100 km in diameter, 800 m thick, and are centered at a depth of 1100 m. Meddy 1 was tracked for two years (1984?86) with five floats as it drifted 1090 km southward with a mean velocity of 1.8 cm s?1. Four shipboard surveys made during these two years revealed the nearly total decay of Meddy 1 by gradual mixing processes. Meddy 2 drifted 530 km southwestward over 8.5 months with a mean velocity of 2.3 cm s?1 until it collided with Hyères Seamount near 31°N, 29°W. The floats trapped in this Meddy then stopped looping abruptly, implying a major disruption of this Meddy. Meddy 3 drifted 500 km southwestward for a year and a half with a mean translation velocity of 1.1 cm s?1. A comparison of the velocity of Meddies to the velocity of nearby floats at 1100 m depth outside of the Meddies shows clearly that all three Meddies moved southwestward through the surrounding water at a speed of about 1.3 cm s?1. The floats inside the Meddies looped anticyclonically in a nearby solid-body rotation with a period of 6 days for Meddy 1, 4 days for Meddy 2, and 5 days for Meddy 3. The rotation period of Meddy 1 appeared to remain constant over nearly two years despite a large decrease in the Meddy's thickness and diameter due to mixing. Rotation velocities in the Meddies were as great as 34 cm s?1 (Meddy 2), much faster than speed of nearby floats outside of the Meddies.