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arXiv · 2605.25501

Long-Term Clustering Pattern of Solar Active Regions and Their Potential Connection with Magneto-Rossby Waves

Junwei Zhao·Ruizhu Chen·Aimee A Norton
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Abstract

Large solar active regions (ARs) tend to be long lived and spatially clustered, with repeated emergence occurring in persistent solar activity nests over extended timescales. By analyzing long-term spatiotemporal magnetic flux maps constructed from near-side magnetic field observations and far-side helioseismic AR maps, we investigate the recurrence and clustering properties of large ARs during Solar Cycle 24. We find that, in both hemispheres, over 63% of magnetic fluxes emerge and cluster within or near three distinct bands in the spatiotemporal maps, two of which rotate faster than the Carrington rate and one more slowly. These bands closely correspond to low-order nonaxisymmetric modes, primarily the azimuthal order m=1 mode. The drift rates of the three spatiotemporal bands are in good agreement with the phase speeds inferred for these modes. The frequencies of the dominant modes are consistent with slow magneto-Rossby waves originating in the solar tachocline, associated with odd harmonic degrees $\ell$ and a toroidal magnetic field strength of approximately 4.0 kG. Our results suggest that magneto-Rossby waves play an important role in modulating both the timing and longitudinal localization of major AR emergence. Rieger-type periodicities may arise from interactions between a dominant mode and weaker modes, while longer quasi-periodic variations on 0.6--4 yr timescales are likely linked to intersections of multiple major modes. These findings point to a potential connection between surface magnetic flux patterns and dynamical processes in the tachocline.

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Junwei Zhao, Ruizhu Chen, Aimee A Norton. 2026-05-25. Long-Term Clustering Pattern of Solar Active Regions and Their Potential Connection with Magneto-Rossby Waves. https://arxiv.org/abs/2605.25501

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