  Euro-Atlantic regimes are typically identified using either the latitude of
the eddy-driven jet, or clustering algorithms in the phase space of 500hPa
geopotential height (Z500). However, while robust trimodality is visibly
apparent in jet latitude indices, Z500 clusters require highly sensitive
significance tests to distinguish them from autocorrelated noise. As a result,
even small shifts in the time-period considered can notably alter the diagnosed
regimes. Fixing the optimal regime number is also hard to justify. We argue
that the jet speed, a near-Gaussian distribution projecting strongly onto the
Z500 field, is the source of this lack of robustness. Once its influence is
removed, the Z500 phase space becomes visibly non-Gaussian, and clustering
algorithms easily recover three extremely stable regimes, corresponding to the
jet latitude regimes. Further analysis supports the existence of two additional
regimes, corresponding to a tilted and split jet. This framework therefore
naturally unifies the two regime perspectives.

Atmospheric and Oceanic Physics