Study of Magnetic Helicity in the Solar Corona

Several new methodologies to detect the magnetic helicity injection activity across the photosphere into the solar corona have been developed recently. We briefly review the basic principle of the typical two methods, the so-called local correlation tracking (LCT) method and the induction equation (IE) method. The reliability of them is examined using a three-dimensional model field. The benchmark examination indicates that, if the vector magnetic field data are available, the IE method can greatly improve the accuracy of the helicity flux measurement. The physical implication of the recent results of the magnetic helicity measurement is also discussed. In particular, we emphasize the possibility that not only the intensity but also the complexity of the magnetic helicity injection from the photosphere could activate the energy liberation process in the solar corona.