Polar flux imbalance at the sunspot cycle minimum governs hemispheric asymmetry in the following cycle
Polar flux imbalance at the sunspot cycle minimum governs hemispheric asymmetry in the following cycle
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DOI：
10.1051/0004-6361/201834425
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发表时间：
2019-06
影响因子：
6.5
通讯作者：
P. Bhowmik
中科院分区：
文献类型：
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作者：
P. Bhowmik
目标。太阳磁活动的半球不规则性是一种观测充分的现象，其成因已通过数值模拟和数据分析技术进行了研究。在这项工作中，我们探讨可能的原因产生南北不对称的反转时间和幅度的极场在周期最小。此外，我们研究半球的不对称性是如何从一个周期到另一个周期翻译的。方法.我们采取了三步走的办法。首先，我们通过分析过去110年的观测资料，探讨了观测到的极区通量和黑子面积的不对称性。其次，我们研究了Babcock-Leighton机制中涉及的各种因素对极地通量的演变和产生的贡献，通过使用表面通量输运模型和合成太阳黑子输入剖面进行数值模拟。第三，翻译半球的不对称性，在接下来的周期估计同化模拟产生的表面磁场图在周期最小的发电机模拟。最后，我们通过进行额外的观测数据驱动的模拟，评估了我们对半球不对称性的理解。结果对观测数据的分析表明，极区通量在周期最小值时的半球不对称性与下一周期的半球总活动之间存在着深刻的联系。我们发现，与太阳黑子的倾斜角的随机性是最关键的元素之间的不同组件的Babcock-Leighton机制在导致半球的不规则性在极场的演变。我们的分析与发电机模拟表明，一个不对称的极向场在太阳极小期可以引入显着的南北不对称的振幅和峰值活动的时间在接下来的周期。虽然观测数据驱动的模拟再现了过去100年来太阳周期中观测到的不对称性的显著特征，但我们推测平均场α效应和纬向环流的波动在这方面的贡献有限。
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.