ISTerre seminar

Dynamo Action in Rotating Shear and Precessional Flows

Thursday 7 May 2026 - 11h00
Ashish Mishra - Helmholtz-Zentrum Dresden-Rossendorf, Dresden, Germany
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Magnetic field generation in rapidly rotating flows at low magnetic Prandtl number (Pm ≪ 1) remains a central challenge in understanding astrophysical and geophysical dynamos. In this talk, I will present recent advances on dynamo action in two canonical systems: Taylor–Couette flows and precession-driven rotating flows.

In Taylor–Couette configurations, we reveal a nonlinear dynamo mechanism that operates at low Pm ≤ 1, a regime previously thought to be unfavorable for sustained magnetic field generation. The system exhibits two distinct dynamo branches: a weak state dominated by large-scale coherent structures and a strong, turbulent state characterized by enhanced magnetic energy and small-scale activity. The transition between these regimes is governed by initial perturbation amplitude, magnetic Prandtl number, and aspect ratio of the cylinder.

Complementarily, in precessional flows, we demonstrate that by suppressing large-scale two-dimensional vortices, three-dimensional inertial waves alone can drive robust dynamo action. This inertial-wave-driven dynamo persists down to Pm∼ 10-3, and Poincaré number Po∼ 0.025, with magnetic field amplification primarily occurring at small scales. Depending on the Reynolds number and Pm, both small-scale and large-scale dynamo regimes are observed.

Together, these results highlight the existence of dynamo action in rotating flows in different configurations and emphasize the critical role of multiscale interactions—from coherent structures to wave-driven turbulence—in enabling magnetic field generation in low-Pm environments relevant to planets, stars, and laboratory experiments.

Organizing team : Géodynamo

Amphithéâtre Killian, Maison des Géosciences, 38400 Saint Martin d'Hères

Informations de visio :

https://univ-grenoble-alpes-fr.zoom.us/j/95211879135?pwd=vW2j9bmx5FI9uyvCifSiSqpxQh9ANV.1