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Contributed talk: Transition from multipolar to dipolar dynamos in stratified systems

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DY2W03 - Modeling, observing and understanding flows and magnetic fields in the Earth's core and in the Sun

Observations of surface magnetic fields of cool stars reveal a large diversity of configurations. Although there is now a consensus that these fields are generated through dynamo processes occurring within the convective zone, the physical mechanism driving such a variety of field topologies is nonetheless in debate. In this talk, we propose to discuss the possible origins of dipole and multipole-dominated morphologies using three-dimensional numerical simulations of stratified systems where the magnetic feedback on the fluid motion is significant. After introducing previous studies focused on understanding the emergence of dipole-dominated or complex multipolar-dominated field topologies, we will show that dipolar solutions can be found at Rossby numbers up to 0.4 in strongly stratified simulations, where previous works suggested that only multipolar fields should exist. We argue that these simulations are reminiscent of the outlier stars observed at Rossby numbers larger than 0.1, whose large-scale magnetic field is dominated by their axisymmetric poloidal component. We analyse how well different proxies can capture the transition in the field morphology in our simulations. Finally, we test their ability to predict the magnetic morphology of a few M-dwarf stars whose internal structure matches that of our simulations and for which homogeneous magnetic field characterisation is available.

This talk is part of the Isaac Newton Institute Seminar Series series.

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