(a) Magnetic flux time evolution of the secondary emerging bipole of AR 12017 (conjugated polarities N2 and P2). The flux measurements are base-differenced to remove the bias of the dispersed preexisting negative flux in the area where the parasitic emergence occurs (see also Figure 3 for the bias). The preexisting bipole N1 P1 was fully emerged for 4 days before the emergence of N2 P2, and it is in its decay phase throughout the time range shown. The orange background marks the time range where emergence of the second bipole has not yet started. Bipole 2 carries half the magnetic flux of bipole 1. (b) Average photospheric Doppler velocities for the nearby QS (dashed) in addition to average Doppler velocities in the collisional PIL (solid curves). The average redshifts in the collisional PIL dominate both the blueshifts and QS average Doppler velocities for the entire period of emergence. (c) Evolution of the flux deficit for bipole 2 including the deficit correction ﹩{{\rm{\Delta }}}_{\mathrm{corr}}﹩ (solid red line; see text for details). Note that a cluster of flare activity begins only when the deficit is increasing. (d) Plot of the oblateness of polarity N2^NS (green), collision distance between N2^NS and the second episode’s P2 (blue), and the PIL length (yellow) with time. Note the rapid increase of the oblateness (from 50% to 80%) for N2^NS after the onset of collision with the second episode within bipole 2. See the text for further discussion.