Abstract
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.