A Lagrangian perspective on jet streams

Synoptic systems are understood to organize heat and momentum transport along jet streams, yet the diagnostics used to identify jets remain fundamentally Eulerian in nature. This creates conceptual tension: if the eddy-driven jet can be meaningfully separated from the synoptic eddies that maintain it, then it must be a persistent flow that Eulerian diagnostics are not designed to isolate. An alternative Lagrangian perspective on jet streams (JetLag) was recently developed and identifies jets not as maxima of wind speed (or derivative variables), but as maxima of isentropic displacement. In this view, jets become persistent features that remain identifiable over synoptic timescales. This definition recovers well-known features of the atmospheric circulation, with some systematic differences relative to Eulerian diagnostics. Here we adopt the Lagrangian definition to revisit jets and their variability using a hierarchy of models, ranging from idealized configurations to reanalyses. We explore the connections between synoptic systems and jets, and those between the upper troposphere and the surface.