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Long-lasting activity complexes (ACs), characterised as a series of closelylocated, continuously emerging solar active regions (ARs), are consideredgenerating prominent poleward surges from observations. The surges lead tosignificant variations of the polar field, which are important for themodulation of solar cycles. We aim to study a prominent poleward surge duringsolar cycle 24 on the southern hemisphere, and analyse its originating ACs andthe effect on the polar field evolution. We automatically identify andcharacterize ARs based on synoptic magnetograms from the Solar DynamicObservatory. We assimilate these ARs with realistic magnetic configuration intoa surface flux transport model, and simulate the creation and migration of thesurge. Our simulations well reproduce the characteristics of the surge and showthat the prominent surge is mainly caused by the ARs belonging to two ACsduring Carrington Rotations 2145-2159 (December 2013-January 2015). The surgehas a strong influence on the polar field evolution of the southern hemisphereduring the latter half of cycle 24. Without the about one-year-long fluxemergence in the form of ACs, the polar field around the cycle minimum wouldhave remained at a low level and even reversed to the polarity at cycle 23minimum. Our study also shows that the long-lived unipolar regions due to thedecay of the earlier emerging ARs cause an intrinsic difficulty ofautomatically identifying and precisely quantifying later emerging ARs in ACs.

Activity Complexes and A Prominent Poleward Surge During Solar Cycle 24