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Polar flux imbalance at the sunspot cycle minimum governs hemispheric asymmetry in the following cycle

Bhowmik, Prantika

Polar flux imbalance at the sunspot cycle minimum governs hemispheric asymmetry in the following cycle Thumbnail


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Abstract

Aims. Hemispheric irregularities of solar magnetic activity is a well-observed phenomenon, the origin of which has been studied through numerical simulations and data analysis techniques. In this work we explore possible causes generating north-south asymmetry in the reversal timing and amplitude of the polar field during cycle minimum. Additionally, we investigate how hemispheric asymmetry is translated from cycle to cycle. Methods. We pursued a three-step approach. Firstly, we explored the asymmetry present in the observed polar flux and sunspot area by analysing observational data of the last 110 years. Secondly, we investigated the contribution from various factors involved in the Babcock–Leighton mechanism to the evolution and generation of polar flux by performing numerical simulations with a surface flux transport model and synthetic sunspot input profiles. Thirdly, translation of hemispheric asymmetry in the following cycle was estimated by assimilating simulation-generated surface magnetic field maps at cycle minimum in a dynamo simulation. Finally, we assessed our understanding of hemispheric asymmetry in the context of observations by performing additional observational data-driven simulations. Results. Analysis of observational data shows a profound connection between the hemispheric asymmetry in the polar flux at cycle minimum and the total hemispheric activity during the following cycle. We find that the randomness associated with the tilt angle of sunspots is the most crucial element among diverse components of the Babcock–Leighton mechanism in resulting hemispheric irregularities in the evolution of polar field. Our analyses with dynamo simulations indicate that an asymmetric poloidal field at the solar minimum can introduce significant north-south asymmetry in the amplitude and timing of peak activity during the following cycle. While observational data-driven simulations reproduce salient features of the observed asymmetry in the solar cycles during the last 100 years, we speculate that fluctuations in the mean-field α-effect and meridional circulation can have finite contributions in this regard.

Citation

Bhowmik, P. (2019). Polar flux imbalance at the sunspot cycle minimum governs hemispheric asymmetry in the following cycle. Astronomy & Astrophysics, 632, Article A117. https://doi.org/10.1051/0004-6361/201834425

Journal Article Type Article
Acceptance Date Oct 25, 2019
Online Publication Date Dec 13, 2019
Publication Date Dec 31, 2019
Deposit Date Nov 12, 2019
Publicly Available Date Dec 18, 2019
Journal Astronomy and astrophysics.
Print ISSN 0004-6361
Electronic ISSN 1432-0746
Publisher EDP Sciences
Peer Reviewed Peer Reviewed
Volume 632
Article Number A117
DOI https://doi.org/10.1051/0004-6361/201834425
Public URL https://durham-repository.worktribe.com/output/1283807

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Copyright Statement
Bhowmik, Prantika (2019). Polar flux imbalance at the sunspot cycle minimum governing hemispheric asymmetry in the following cycle. Astronomy & Astrophysics 632: A117, reproduced with permission © ESO.






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