Where does eddy collide?

In physical oceanography, an eddy is a coherent rotating vortex of water, typically tens to a few hundred kilometres across, that pinches off from meandering currents and drifts for weeks to months while trapping and transporting heat, salt, and biota within its core. Chelton, Schlax, and Samelson's 2011 Global observations of nonlinear mesoscale eddies used satellite altimetry to show these features are ubiquitous and that most are nonlinear, carrying their trapped water with them. The referent is a rotating parcel of ocean water characterised by its radius, swirl speed, and propagation, and it is a different thing from circulating currents induced in a metal, sharing only the word borrowed from the swirl of a stream.[1]

Unit

The radius, rotational speed, and lifetime of a rotating water vortex

Recovery means

Not applicable

Measured by

Detected and tracked from sea-surface-height anomalies in satellite altimetry, with swirl speed from geostrophy and cores sampled in situ

In electromagnetism, an eddy current is a loop of electric current induced within a bulk conductor by a changing magnetic field, flowing in closed paths perpendicular to the field in accordance with Faraday's and Lenz's laws and dissipating energy as resistive heat. Griffiths's Introduction to electrodynamics develops the induced circulating currents that underlie magnetic braking, induction heating, and non-destructive testing. The word was borrowed by analogy to the swirls of a fluid, but the referent is an induced circulation of charge in a solid, quantified by current density and power loss, and it is unrelated to a rotating body of seawater.[2]

Unit

The induced current density and the power dissipated in the conductor

Recovery means

Not applicable

Measured by

Characterised by induced current density, resistive power loss, and skin depth; probed in practice by eddy-current testing of conductive parts