A 22-Year Cycle of the Network Topology for Solar Active Regions

TL;DR

This study uses complex network analysis to compare solar active regions across four solar cycles, revealing a 22-year Hale cycle pattern in the network topology that reflects underlying solar magnetic activity.

Contribution

The paper introduces a novel application of complex network analysis to solar active regions, uncovering a 22-year cycle in network properties linked to solar magnetic activity.

Findings

Degree distribution follows a power law in each cycle.

Higher characteristic exponents in even cycles.

Identification of a 22-year Hale cycle in network topology.

Abstract

In this paper, solar cycles 21 to 24 were compared using complex network analysis. A network was constructed for these four solar cycles to facilitate the comparison. In these networks, the nodes represent the active regions of the Sun that emit flares, and the connections correspond to the sequence of solar flares over time. This resulted in a directed network with self-connections allowed. The model proposed by Abe and Suzuki for earthquake networks was followed. The incoming degree for each node was calculated, and the degree distribution was analyzed. It was found that for each solar cycle, the degree distribution follows a power law, indicating that solar flares tend to appear in correlated active zones rather than being evenly distributed. Additionally, a variation in the characteristic exponent {\gamma} for each cycle was observed, with higher values in even cycles compared to odd cycles. A more detailed analysis was performed by constructing 11-year networks and shifting them in one-year intervals. This revealed that the characteristic exponent shows a period of approximately 22 years coincident with the Hale cycle, suggesting that the complex networks provide information about the solar magnetic activity.