Chapter 7 A study of meddies using simultaneous in-situ and satellite observations

Abstract

Abstract Data from the National Oceanic and Atmospheric Administration (NOAA) and Topography Experiment (TOPEX)JPoseidon (TJP) satellites, a surface drifter, and subsurface floats, named RAFOS, at a depth of -1000 m in the Mediterranean Undercurrent were used to investigate Mediterranean Water eddies, or meddies, off the southwest coast of Portugal. Analysis of RAFOS trajectories and simultaneous distributions of NOAA Advanced Very-High Resolution Radiometer (AVHRR) sea surface temperature (SST) and TJP sea level anomalies revealed that meddies frequently have a signature in the surface thermal field. Characteristics of these signatures include clockwise wrapping of filament structures around the eddy periphery and higher sea level anomalies of -10 cm. A sequence of six SST images, taken between 14 March and 2 May 1994, was compared with contemporaneous 11-day trajectories of selected RAFOS floats to investigate the eddy-like features of the SST field in relation to eddy motion in the Mediterranean Undercurrent. The structure and evolution of submesoscale cyclonic and anticyclonic structures identified in the SST field were found to reflect mid-depth flow structures with similar features, as revealed by the RAFOS trajectories. This approach yielded relevant clues to the interpretation of the movement of meddies: namely, their irregular trajectories with stops and sudden changes in direction that could be attributed to their interaction with other vortices.