Magnetic Helicity, Coronal Heating and Solar Flaring Activity: A Review of the Role of Active Region Twist

Magnetic helicity of solar active regions is quantified by the twist and writhe of their underlying flux tubes. The twist component, in particular, is believed to be an important determinant of the energetics and dynamics of active regions that ultimately lead to coronal heating and solar eruptive activity. Here, I review the role of active region twist in the context of solar activity – laying emphasis on constraints that are set by observations. The results, taken cumulatively, suggests a new paradigm. In this paradigm, the distribution and evolution of twist in active region sub-structures play a more predominant role in driving solar dynamic activity than the magnitude of the global active region twist itself. I discuss the implications of these observational constraints for theories of stellar coronal heating and solar eruptive activity.