Aggregation Characteristics of the Sun’s Large-Scale Magnetic Field Associated with a Global Magnetic Anomaly in the Last Extended Solar Cycle

The solar cycle represents the Sun’s periodically changing magnetic state, which is potentially subject to global magnetic anomalies emerging on it. What the characteristics are of the Sun’s large-scale magnetic field playing roles in these anomalies is a key to clarifying how the Sun deviates from its normal magnetic state. This article reports aggregation characteristics of the large-scale magnetic field associated with a global magnetic anomaly that emerged when the Sun went through one of the longest solar cycles in two hundred years. The characteristics were identified by extracting cluster feature values of solar surface magnetic fields via a population ecological method from synoptic maps, obtained by the longest homogeneous series of magnetic field observations for the past several decades. We found that the anomaly was due to the uneven clustering of positive and negative surface magnetic fields that occurred during the solar minimum leading to the last extended solar cycle. Our findings may provide new insight into magnetic field characteristics peculiar to a solar minimum with an extended cycle length.