Variations in the Solar Magnetic Fields and their Influence on Coronal Mass Ejections and Type-II Radio Bursts

The parameters of type-II radio bursts (RBIIs) and coronal mass ejections (CMEs) associated with them (the so-called radio-loud CMEs (RL CMEs)) in solar cycles 23 and 24 (1997–2017) are analyzed based on data from ground-based and space-borne observations. The dependences of these parameters on the strength of the global magnetic field (GMF) in the region of RBIIs and the degree of GMF structural variability are also studied. The results show that both the polar and nonpolar components of the solar GMF decrease from cycle 23 to cycle 24. At the same time, the GMF structure becomes more chaotic. Since the GMF magnitude is lower in cycle 24, the dependences of all parameters of RL CMEs and RBIIs are shifted toward lower values of the GMF. Most events form under a stable GMF structure. While the total number of CMEs increased from 13 924 in cycle 23 to 15 074 in cycle 24, the number of RL CMEs decreased from 338 in cycle 23 to 180 in cycle 24. Parameters of RL CMEs and PBIIs differ in cycles 23 and 24 and the nature of their change corresponds to powerful CMEs and the dynamics of magnetic fields above 100 G. The presence of separate groups of RL CMEs and RBIIs in the dependencies on the GMF magnitude and structural variability can serve as evidence of different kinds of RBIIs, the formation of which requires completely different conditions.