On Polar Magnetic Field Reversal in Solar Cycles 21, 22, 23, and 24

TL;DR

This study analyzes the timing and characteristics of polar magnetic field reversals across Solar Cycles 21 to 24, revealing hemisphere-specific reversal sequences, their relation to sunspot activity and heliospheric tilt, and predicting Cycle 25 strength.

Contribution

It provides a detailed comparison of polar reversal epochs with sunspot activity, HCS tilts, and hemispheric asymmetries, and introduces a method to estimate the upcoming solar cycle's amplitude.

Findings

Reversals occurred near sunspot maxima in Cycles 21 and 23, and after maxima in Cycles 22 and 24.

Reversal times differ between hemispheres, with the N-hemisphere reversing earlier.

Predicted Solar Cycle 25 amplitude to be approximately 116, similar to Cycle 24.

Abstract

The Sun's polar magnetic fields change their polarity near the maximum of sunspot activity. We analyzed the polarity reversal epochs in Solar Cycles 21 to 24. There was a triple reversal in the N-hemisphere in Solar Cycle 24 and single reversals in the rest of cases. Epochs of the polarity reversal from measurements of the Wilcox Solar Observatory (WSO) are compared with ones when the reversals were completed in the N- and S-hemispheres. The reversal times were compared with hemispherical sunspot activity and with the Heliospheric Current Sheet (HCS) tilts, too. It was found that reversals occurred at the epoch of the sunspot activity maximum in Cycles 21 and 23, and after the corresponding maxima in Cycles 22 and 24, and one-two years after maximal HCS tilts calculated in WSO. Reversals in Solar Cycles 21, 22, 23, and 24 were completed first in the N-hemisphere and then in the S-hemisphere after 0.6, 1.1, 0.7, and 0.9 years, respectively. The polarity inversion in the near-polar latitude range \pm(55-90)^\circ occurred from 0.5 to 2.0 years earlier that the times when the reversals were completed in corresponding hemisphere. Using the maximal smoothed WSO polar field as precursor we estimated that amplitude of Solar Cycle 25 will reach 116 \pm 12 in values of smoothed monthly sunspot numbers and will be comparable with the current cycle amplitude equaled to 116.4.