Figure 1 shows the horizontal velocity pattern of photospheric features in the main part of active region NOAA 9077 on 2000 July 12 – 15, where the horizontal velocity vectors are overlapped by white light images (left) and contours represent $G=-2{\bf U}\cdot {\bf A_p}B_n$ (injective rate of magnetic helicity) inferred from the horizontal velocity vectors and longitudinal magnetic field (right). The black (white) contours with white (black) areas mark the positive (negative) change rate of magnetic helicity of $\pm$5, 20, 50, 100, 180, 300 ($\times 10^{13}G^2m^2s^{-1}$). The arrows overlapped by $G$ mark the transverse magnetic field.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html