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In order to understand whether major flares or coronal mass ejections (CMEs)can be related to changes in the longitudinal photospheric magnetic field, westudy 4 young active regions during seven days of their disc passage. This timeperiod precludes any biases which may be introduced in studies that look at thefield evolution during the short-term flare or CME period only. Data from theMichelson Doppler Imager (MDI) with a time cadence of 96 minutes are used.Corrections are made to the data to account for area foreshortening and anglebetween line of sight and field direction, and also the underestimation of theflux densities. We make a systematic study of the evolution of the longitudinalmagnetic field, and analyze flare and CME occurrence in the magnetic evolution.We find that the majority of CMEs and flares occur during or after new fluxemergence. The flux in all four active regions is observed to have deviationsfrom polarity balance both on the long-term (solar rotation) and on the shortterm (few hours). The long-term imbalance is not due to linkage outside theactive region; it is primarily related to the east-west distance from centralmeridian, with the sign of polarity closer to the limb dominating. The sequenceof short term imbalances are not closely linked to CMEs and flares and nopermanent imbalance remains after them. We propose that both kinds of imbalanceare due to the presence of a horizontal field component (parallel to thephotospheric surface) in the emerging flux.Comment: 22 pages, 8 figures, Solar Physics (in press

How are Emerging Flux, Flares and CMEs Related to Magnetic Polarity Imbalance in MDI Data?