An analysis of the evolution of Meddies in the North Atlantic using floats and multisensor satellite data

Abstract

Previous studies focusing on the remote detection of Mediterranean Eddies (Meddies) have reported that the isopycnal surface changes derived from satellite multisensor measurements at the approximate depth of 400 m can be used to sense the presence of underlying Meddies. While the isopycnal surface near that depth does indeed reveal the locations of Meddies, an analysis of isopycnal surface changes in response to the evolution of Meddies has yet to be made. Accordingly, this research focuses on analyzing the relationship between isopycnal surface changes and the evolution of Meddies. The vertical isopycnal surface variability of Meddies, which is directly related to contributions from rotational velocity, interior thermal variation, and vertical displacement of Meddies, is observed and studied using float observations from A Mediterranean Undercurrent Seeding Experiment (AMUSE). The contributions of each of the three aforementioned parameters are estimated, enabling us to understand their relative role in changing the isopycnal surface above Meddies. Furthermore, in order to further understand Meddies' evolution and their associated forcing, the dominant frequencies of their horizontal and vertical displacements, as well as the sea surface height variability above the Meddy, are analyzed using the Hilbert-Huang Transform. Finally, the horizontal and the vertical eddy viscosity dissipation of Meddies is computed and compared with a theoretical model. The empirical horizontal and the vertical eddy viscosities are found to be 7 3 10 6 cm 2 s 21 and 200 cm 2 s 21 , respectively. This study will therefore contribute to understanding how the isopycnal surface is related to the presence of Meddies, what frequencies dominate its variability, and the values of eddy viscosity which can be used for a numerical model.

First evidence of European eels exiting the Mediterranean Sea during their spawning migration

“…However, despite this limitation, it was clear that all the eels migrated south-west in the direction of the Gibraltar Strait, and two eels escaped to the Atlantic during their time at liberty. Once out of the Mediterranean, one of the eels (tag 133986) performed a loop that may be related to a mesoscale eddy, commonly generated in the Mediterranean outflow 22 .…”

Meddies and Their Sea Surface Expressions: Observations and Theory

“…In what was perhaps the first published mention of meddies' manifestation at the sea surface, Käse and Zenk (1987) demonstrated a tendency of a surface drifter to make a semicircle in a clockwise direction over an observed meddy. Since then, ample evidence of meddies forming a measurable dynamic signature at the sea surface has been collected (Stammer et al 1991;Pingree and Le Cann 1993a;Oliveira et al 2000;Paillet et al 2002;Bashmachnikov et al 2009;Jo et al 2015;Ciani et al 2015, among others).…”