Solar Activity Studies using Microwave Imaging Observations

TL;DR

This study uses microwave imaging observations to analyze solar cycle 24, revealing polar magnetic field behavior, asymmetries, and implications for future sunspot activity based on polar prominence eruptions and brightness enhancements.

Contribution

It demonstrates the correlation between microwave brightness enhancements and polar magnetic fields, providing insights into solar cycle progression and hemispheric asymmetries.

Findings

North polar region had near-zero magnetic field from 2012 to 2015.

Polar MBE correlates strongly with polar magnetic field strength.

Polar field of one cycle predicts the next cycle's sunspot activity.

Abstract

We report on the status of solar cycle 24 based on polar prominence eruptions (PEs) and microwave brightness enhancement (MBE) information obtained by the Nobeyama radioheliograph. The north polar region of the Sun had near-zero field strength for more than three years (2012 to 2015) and ended only in September 2015 as indicated by the presence of polar PEs and the lack of MBE. The zero-polar-field condition in the south started only around 2013, but it ended by June 2014. Thus the asymmetry in the times of polarity reversal switched between cycle 23 and 24. The polar MBE is a good proxy for the polar magnetic field strength as indicated by the high degree of correlation between the two. The cross-correlation between the high- and low-latitude MBEs is significant for a lag of ~5.5 to 7.3 years, suggesting that the polar field of one cycle indicates the sunspot number of the next cycle in agreement with the Babcock-Leighton mechanism of solar cycles. The extended period of near-zero field in the north-polar region should result in a weak and delayed sunspot activity in the northern hemisphere in cycle 25.