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Unusual Polar Conditions in Solar Cycle 24 and their Implications for Cycle 25

We report on the prolonged solar-maximum conditions until late 2015 at the north-polar region of the Sun indicated by the occurrence of high-latitude prominence eruptions and microwave brightness temperature close to the quiet Sun level. These two aspects of solar activity indicate that the polarity reversal was completed by mid-2014 in the south and late 2015 in the north. . The microwave brightness in the south-polar region has increased to a level exceeding the level of cycle 23/24 minimum, but just started to increase in the north. The north-south asymmetry in the polarity reversal has switched from that in cycle 23. These observations lead us to the hypothesis that the onset of cycle 25 in the northern hemisphere is likely to be delayed with respect to that in the southern hemisphere. We find that the unusual condition in the north is a direct consequence of the arrival of poleward surges of opposite polarity from the active region belt. We also find that multiple rush-to-the-pole episodes were indicated by the prominence eruption locations that lined up at the boundary between opposite polarity surges. The high-latitude prominence eruptions occurred in the boundary between the incumbent polar flux and the insurgent flux of opposite polarity.