Evolution of Magnetic Helicity in Solar Cycle 24

Abstract

We propose a novel approach to reconstruct the surface magnetic helicity density on the Sun or sun-like stars. The magnetic vector potential is determined via decomposition of vector magnetic field measurements into toroidal and poloidal components. The method is verified using data from a non-axisymmetric dynamo model. We apply the method to vector field synoptic maps from Helioseismic and Magnetic Imager (HMI) onboard of Solar Dynamics Observatory (SDO) to study evolution of the magnetic helicity density during solar cycle 24. It is found that the mean helicity density of the non-axisymmetric magnetic field of the Sun evolves in a way which is similar to that reported for the current helicity density of the solar active regions. It has predominantly the negative sign in the northern hemisphere, and it is positive in the southern hemisphere. Also, the hemispheric helicity rule for the non-axisymmetric magnetic field showed the sign inversion at the end of cycle 24. Evolution of magnetic helicity density of large-scale axisymmetric magnetic field is different from that expected in dynamo theory. On one hand, the mean large- and small-scale components of magnetic helicity density display the hemispheric helicity rule of opposite sign at the beginning of cycle 24. However, later in the cycle, the two helicities exhibit the same sign in contrast with the theoretical expectations.

arXiv comment8 pages 5 figures

References in corpus (12)

• Astrophysical magnetic fields and nonlinear dynamo theory
• Dynamic nonlinearity in large scale dynamos with shear
• Doubly Helical Coronal Ejections from Dynamos and their Role in Sustaining the Solar Cycle
• Scale-dependence of magnetic helicity in the solar wind
• New dynamo pattern revealed by solar helical magnetic fields
• Two-scale analysis of solar magnetic helicity
• The magnetic field vector of the Sun-as-a-star. II. Evolution of the large-scale vector field through activity cycle 24
• The origin of the helicity hemispheric sign rule reversals in the mean-field solar-type dynamo
• Bihelical spectrum of solar magnetic helicity and its evolution
• Magnetic helicity of global field in cycles 23 and 24
• Does nonaxisymmetric dynamo operate in the Sun?
• Structure and evolution of the photospheric magnetic field in 2010 - 2017: comparison of SOLIS/VSM vector field and $B_{LOS}$ potential field

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