Magnetic Helicity Reversals in a Cyclic Convective Dynamo

Abstract

We investigate the role of magnetic helicity in promoting cyclic magnetic activity in a global, 3D, magnetohydrodynamic (MHD) simulation of a convective dynamo. This simulation is characterized by coherent bands of toroidal field that exist within the convection zone, with opposite polarities in the northern and southern hemispheres. Throughout most of the cycle, the magnetic helicity in these bands is negative in the northern hemisphere and positive in the southern hemisphere. However, during the declining phase of each cycle, this hemispheric rule reverses. We attribute this to a global restructuring of the magnetic topology that is induced by the interaction of the bands across the equator. This band interaction appears to be ultimately responsible for, or at least associated with, the decay and subsequent reversal of both the toroidal bands and the polar fields. We briefly discuss the implications of these results within the context of solar observations, which also show some potential evidence for toroidal band interactions and helicity reversals.

arXiv comment6 pages, 4 color figures, accepted to Astrophysical Journal Letters

References in corpus (8)

• Astrophysical magnetic fields and nonlinear dynamo theory
• Global-Scale Turbulent Convection and Magnetic Dynamo Action in the Solar Envelope
• Persistent Magnetic Wreaths in a Rapidly Rotating Sun
• Magnetic Cycles in a Convective Dynamo Simulation of a Young Solar-type Star
• Grand Minima and Equatorward Propagation in a Cycling Stellar Convective Dynamo
• Equatorial magnetic helicity flux in simulations with different gauges
• Global Twist of Sunspot Magnetic Fields Obtained from High Resolution Vector Magnetograms
• Hemispheric Helicity Trend for Solar Cycle 24

Cited by in corpus (6)

• Threshold of non-potential magnetic helicity ratios at the onset of solar eruptions
• Time variations of the non-potential and volume-threading magnetic helicities
• Automated Swirl Detection Algorithm (ASDA) and Its Application to Simulation and Observational Data
• Synthetic solar cycle for active regions violating the Hale's polarity law
• The Rise of a Magnetic Flux Tube in a Background Field: Solar Helicity Selection Rules
• Dynamos and Differential Rotation: Advances at the Crossroads of Analytics, Numerics, and Observations