Magnetic field line topology in solar active regions

According to a recent study comparing magnetic fields extrapolated from photospheric measurements with chromospheric and coronal observations, the electric current helicity in active regions possesses a predominant sign in each of the two solar hemispheres. This indicates that the generation of atmospheric electric currents, which are needed as the energy source for flares and coronal heating, is a global phenomenon connected with the rotation of the Sun rather than a consequence of plasma motions within individual active regions uncorrelated between different active regions. Theoretically, the evolution of the atmospheric magnetic field may be understood as the continual distortion of an existing equilibrium by disturbances propagating upward from the photosphere and subsequent fast relaxation to a new, neighboring equilibrium. Here current helicity proves to be an important quantity decisive for whether the (mean) magnetic field can evolve along a stable path with growing free energy. Disruptive disturb...