Twisted solar active region magnetic fields as drivers of space weather: Observational and theoretical investigations

The properties and dynamics of magnetic fields on the Sun's photosphere and outer layers-notably those within solar active regions-govern the eruptive activity of the Sun. These photospheric magnetic fields also act as the evolving lower boundary of the Sun-Earth coupled system. Quantifying the physical attributes of these magnetic fields and exploring the mechanisms underlying their influence on the near-Earth space environment are of vital importance for forecasting and mitigating adverse space weather effects. In this context, we discuss here a novel technique for measuring twist in the magnetic field lines of solar active regions that does not invoke the force-free field assumption. Twist in solar active regions can play an important role in flaring activity and the initiation of CMEs via the kink instability mechanism; we outline a procedure for determining this solar active region eruptive potential. We also discuss how twist in active region magnetic fields can be used as inputs in simulations of the coronal and heliospheric fields; specifically, we explore through simulations, the formation, evolution and ejection of magnetic flux ropes that originate in twisted magnetic structures. The results and ideas presented here are relevant for exploring the role of twisted solar active region magnetic fields and flux ropes as drivers of space weather in the Sun-Earth system. (c) 2007 Elsevier Ltd. All rights reserved.