Synoptic observation of a full mesoscale eddy lifetime and its secondary instabilities in the Gulf of Mexico

Abstract. Mesoscale eddies are crucial to ocean circulation, climate, and tracer transport. Yet their life cycle has never been observed synoptically at high resolution. In this study, I use novel SWOT satellite altimetry data to present the first synoptic characterization of a loop current eddy's life cycle in the Gulf of Mexico, during a 6-month period. SWOT allows for the direct observation of key dynamical processes – such as eddy shielding, high-mode instabilities, and dipolar interactions – that were previously only partially resolved in interpolated altimetry products and mainly described in theoretical or numerical studies. These observations challenge the traditional view of eddies as simple, elliptical structures, emphasizing the role of mesoscale interactions in their evolution. Furthermore, SWOT captures intense submesoscale turbulence at the eddy's rim, revealing secondary instabilities likely driving its decay. These findings not only validate decades of vortex theory but also offer new insights into oceanic turbulence dynamics.