Extended Data Fig. 5: PDF of cosine of angle between u, b, ω(= ∇ × u), and j(= ∇ × b), in a simulation with 4096 × 4096 × 8192 grid points. | Nature

Extended Data Fig. 5: PDF of cosine of angle between u, b, ω(= ∇ × u), and j(= ∇ × b), in a simulation with 4096 × 4096 × 8192 grid points.

From: Large-scale dynamos driven by shear-flow-induced jets

Extended Data Fig. 5

The turbulent flow and fields measured at the shear layer are non-helical and close to pure Alfvénic states (orange curve), which explains why the ϒ-effect dominates in the mean EMF. For the pure Alfvénic states, α is zero; β and ϒ are similar and are not impacted by the non-kinematic (flow-evolution) effect in the same manner as the α is (see last paragraph of “Analytic quasilinear EMF model” in Methods). A large-scale steady shear flow induces an “imbalanced” MHD turbulence (asymmetry of the orange curve) and thus drives the dynamo via the non-zero ϒ-coefficient. Similar PDFs of dominant cross-helicity and non-helical flows were recently detected in the magnetosheath turbulence observed by the Magnetospheric Multiscale Spacecraft49.

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