Current helicity quantifies the location of twisted and sheared nonpotential structures in a magnetic field. We simulate the evolution of magnetic fields in the solar atmosphere in response to flux emergence and shearing by photospheric motions. In our global-scale simulation over many solar rotations, the latitudinal distribution of current helicity develops a clear statistical pattern, matching the observed hemispheric sign at active latitudes. In agreement with observations, there is significant scatter and intermixing of both signs of helicity, where we find local values of current helicity density that are much higher than those predicted by linear force-free extrapolations. Forthcoming full-disk vector magnetograms from the Solar Dynamics Observatory will provide an ideal opportunity to test our theoretical results on the evolution and distribution of current helicity, both globally and in single active regions.
Yeates, A., Mackay, D., & van Ballegooijen, A. (2008). Evolution and distribution of current helicity in full-Sun simulations. Astrophysical Journal Letters, 680(2), L165-L168. https://doi.org/10.1086/590057