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Journal Article

Differences in the solar cycle variability of simple and complex active regions during 1996–2018


Käpylä,  Maarit J.
Department Sun and Heliosphere, Max Planck Institute for Solar System Research, Max Planck Society;

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Nikbakhsh, S., Tanskanen, E. I., Käpylä, M. J., & Hackman, T. (2019). Differences in the solar cycle variability of simple and complex active regions during 1996–2018. Astronomy and Astrophysics, 629: A45. doi:10.1051/0004-6361/201935486.

Cite as: https://hdl.handle.net/21.11116/0000-0006-6817-C
Aims. Our aim is to examine the solar cycle variability of magnetically simple and complex active region.

Methods. We studied simple (α and β) and complex (βγ and βγδ) active regions based on the Mount Wilson magnetic classification by applying our newly developed daily approach. We analyzed the daily number of the simple active regions (SARs) and compared that to the abundance of the complex active regions (CARs) over the entire solar cycle 23 and cycle 24 until December 2018.

Results. We show that CARs evolve differently over the solar cycle from SARs. The time evolution of SARs and CARs on different hemispheres also shows differences, even though on average their latitudinal distributions are shown to be similar. The time evolution of SARs closely follows that of the sunspot number, and their maximum abundance was observed to occur during the early maximum phase, while that of the CARs was seen roughly two years later. We furthermore found that the peak of CARs was reached before the latitudinal width of the activity band starts to decease.

Conclusion. Our results suggest that the active region formation process is a competition between the large-scale dynamo (LSD) and the small-scale dynamo (SSD) near the surface, the former varying cyclically and the latter being independent of the solar cycle. During solar maximum, LSD is dominant, giving a preference to SARs, while during the declining phase the relative role of SSD increases. Therefore, a preference for CARs is seen due to the influence of the SSD on the emerging flux.