Magnetic helicity as a probe of magnetic flux-tube dynamics in the solar interior

Magnetic helicity (volume integral of the product of the magnetic field vector B and the vector potential A ), or its proxy, the current helicity at the surface (surface integral of B . J or B _z J _z ), is an important quantity which characterizes the helical nature of solar magnetic fields. The current helicity on the Sun shows a tendency, though with large dispersion, that it is positive in the southern hemisphere and negative in the northern hemisphere (the helicity sign rule). However, there are indications that the helicity sign rule may be reversed at activity minimum periods. We will discuss the significance of this property by focusing on the statistical distributions of helicity whether its dispersion follows Gaussian distribution or not.