Another Mini Solar Maximum in the Offing: A Prediction for the Amplitude of Solar Cycle 25

Abstract

We examine the temporal changes in both solar polar magnetic field (PMF) at latitudes ≥45° and heliospheric magnetic field (HMF) at 1 AU during solar cycles 21–24 with emphasis on the recent activity changes after July 2015, the so called “mini solar maximum” of cycle 24. While unsigned PMF shows solar cycle modulations in cycles 21 and 22, it shows an anti-correlation with solar cycle variation in cycle 24. In addition, the floor level of the HMF (of 4.6 nT), that is, the value that the HMF returns to at each solar minimum, is breached about 2 years prior to cycle 24 minimum, indicating a reduced HMF floor level of 3.2 ± 0.5 nT in the upcoming cycle 24 minimum. In light of the change of unsigned PMF and the availability of a revised smoothed sunspot number (SSN V2.0) after July 2015, we revisit the correlation of unsigned PMF and HMF at solar minimum. The correlation is used to estimate values of the HMF at the cycle 24 minimum and the amplitude of the upcoming cycle 25. The updated prediction is 134 ± 11 or 131 ± 11 on the revised SSN V2.0 scale assuming the cycle 24 minimum to occur in 2020 or 2021, respectively. The SSN values indicate that the cycle 25 will be stronger than cycle 24 and a little weaker than cycle 23, even if the current solar cycle minimum occurs in 2021 instead of 2020. This implies that we will witness another mini solar maximum in the upcoming cycle 25.