  As an observational case study, we consider the origin of a prominent
poleward surge of leading polarity, visible in the magnetic butterfly diagram
during Solar Cycle 24. A new technique is developed for assimilating individual
regions of strong magnetic flux into a surface flux transport model. By
isolating the contribution of each of these regions, the model shows the surge
to originate primarily in a single high-latitude activity group consisting of a
bipolar active region present in Carrington Rotations 2104-05 (November
2010-January 2011) and a multipolar active region in Rotations 2107-08
(February-April 2011). This group had a strong axial dipole moment opposed to
Joy's law. On the other hand, the modelling suggests that the transient
influence of this group on the butterfly diagram will not be matched by a large
long-term contribution to the polar field, because of its location at high
latitude. This is in accordance with previous flux transport models.
