The solar activities such as solar flares and coronal mass ejections (CMEs) tend to occur at sunspot group (active region) with complex topology of magnetic fields. The number of sunspots varies according to the approximately 11-year solar cycle and the sun's magnetic field changes polarity approximately every 11 years. Solar magnetic field is believed to be excited by solar dynamo mechanism in the convection zone of the sun. Various dynamo models have been suggested for the solar cycle. However, identification of particular details of solar dynamo with surface manifestation of solar dynamo accessible for observations remains a disputable problem.The twist and shear of magnetic fields cause their non-potentiality and the store of magnetic free energy, which release process relates to the solar flare-CMEs.Helicity is a measure of the complexity of the magnetic field topology.Therefore, the study of solar magnetic helicity is important for the study of non-potential of magnetic field, solar activity and solar dynamo theory.In recent years, there have been significant advances in the study of magnetic structure and evolution, solar eruption, owing to the availability of grand- and space-base observations and the development of advanced data analysis and modeling tools.
In this session, we will focus on the diagnose ofsolar magnetic fields;the developments and evolution of solar magnetic fields in active regions and the relationship with solar cycle;the spatial topology ofsolar magnetic fieldswith solar eruptive phenomena; new progress and future development trend of solar magnetic field observational instruments.