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Dependence of Convective Dynamo Action on Bulk Electrical Conductivity
  • Krista Soderlund,
  • Jonathan Aurnou
Krista Soderlund
University of Texas at Austin

Corresponding Author:[email protected]

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Jonathan Aurnou
University California, Los Angeles
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Convective dynamo action may be fundamentally different between low-mass and high-mass stars due to a dichotomy in their bulk electrical conductivities relative to kinematic viscosity as characterized by the magnetic Prandtl number, Pm (Augustson et al., 2019, https://doi.org/10.3847/1538-4357/ab14ea). Magnetic Prandtl values less than unity are expected in low-mass stars with convective envelopes, while larger Pm values are more relevant for high-mass stars with convective cores. Here we investigate how the fluid’s electrical conductivity alters the behavior of a given dynamo system through a suite of 3D, spherical shell dynamo models in the strongly-forced convective regime with varied magnetic Prandtl number. We find that the fluid motions, the pattern of convective heat transfer, and the mode of dynamo generation all differ across the range 0.25 ≤ Pm ≤ 10. For example, we show that strong magnetohydrodynamics effects cause a fundamental change in the surface zonal flows: the equatorial zonal jet reverses direction for sufficiently large values of the electrical conductivity. Thus, our work further supports the importance of bulk electrical conductivity for not only sustaining dynamo action, but also for the characteristics of the large-scale convective flows that generate those dynamo fields.