Fraser Goldsworth has published the first paper from his DPhil in the Journal of Physical Oceanography, demonstrating how boundary currents become “symmetrically unstable” upon crossing the equator. Using a hierarchy of models, he investigates how symmetric instability might manifest itself if excited in cross-equatorial flows. He finds that when the instability is excited, it generates stacked overturning cells which reorganise the current to make it neutrally stable to symmetric instability. This process is likely to be occurring in the Atlanticcean off the coast of Brazil where, indeed, there is some observational evidence for the “smaoking gun” of symmetric instability (zero potential vorticity).

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