Observations of Magnetic Helicity Proxies in the Solar Photosphere: Helicity With Solar Cycles

Observations of magnetic helicity transportation through the solar photosphere reflect the interaction of turbulent plasma movements and magnetic fields in the solar dynamo process. In this chapter, we review the research on magnetic helicity inferred from observed solar magnetic fields in the photosphere and solar morphological configurations with solar cycles. After introducing some achievements in the study of magnetic helicity, we summarize several key points. The magnetic (current) helicity in the solar surface layer presents a statistical distribution similar to that of a sunspot butterfly diagram, but its maximum value is delayed compared to the extreme value of the sunspot butterfly diagram and corresponds to the phase with the statistical eruption of solar flares. During the spatial transport of magnetic (current) helicity from the interior of the Sun into interplanetary space at the time-space scale of the solar cycle, the helicity shows a statistical distribution and fluctuation with the hemispheric sign rule. These show that the current helicity and magnetic helicity transport calculation methods complement each other. We also see that the study of the inherent relationship between magnetic helicity and the solar cycle depends on the observed accuracy of the solar magnetic field.