Mesoscale Eddy

A mesoscale eddy is a coherent rotating ocean vortex with a horizontal scale of tens to a few hundred kilometers, set by the first baroclinic Rossby radius of deformation, and a lifetime of weeks to over a year. Surface speeds reach tens of centimeters per second, and altimetry tracks thousands of them globally. They form mainly by baroclinic instability of fronts and boundary currents, releasing available potential energy into eddy kinetic energy, and they carry trapped water masses, heat, and biogeochemical tracers across the mean flow. Mesoscale eddies hold most of the ocean’s kinetic energy.