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Understanding the nature and evolution of the photospheric helicity fluxtransfer is a key to reveal the role of magnetic helicity in coronal dynamicsof solar active regions. Using SDO/HMI photospheric vector magnetograms and thederived flow velocity field, we computed boundary driven helicity flux with a12 minute cadence during the emergence of AR 11928. Accounting the foot pointconnectivity defined by non-linear force-free magnetic extrapolations, wederived and analyzed the corrected distribution of helicity flux maps. Thephotospheric helicity flux injection is found to changes sign during the steadyemergence of the AR. This reversal is confirmed with the evolution of thephotospheric electric currents and with the coronal connectivity as observed inEUV wavelengths with SDO/AIA. During about the three first days of emergence,the AR coronal helicity is positive while later on the field configuration isclose to a potential field. As theoretically expected, the magnetic helicitycancelation is associated to enhanced coronal activity. The study suggests aboundary driven transformation of the chirality in the global AR magneticstructure. This may be the result of the emergence of a flux rope with positivetwist around its apex while it has negative twist in its legs. The origin ofsuch mixed helicity flux rope in the convective zone is challenging for models.

Successive Injection of Opposite Magnetic Helicity in Solar Active Region NOAA 11928