Decay and dispersal of the tilted Bipolar Magnetic Regions (BMRs) on the solar surface are observed to produce the large-scale poloidal field, which acts as the seed for the toroidal field and, thus, the next sunspot cycle. However, various properties of BMR, namely, the tilt, time delay between successive emergences, location, and flux, all have irregular variations. Previous studies show that these variations can lead to changes in the polar field. In this study, we first demonstrate that our 3D kinematic dynamo model, STABLE, reproduces the robust feature of the surface flux transport (SFT) model, namely the variation of the generated dipole moment with the latitude of the BMR position. Using STABLE in both SFT and dynamo modes, we perform simulations by varying the individual properties of BMR and keeping their distributions the same in all the cycles as inspired by the observations. We find that randomness due to the distribution in either the time delay or the BMR latitude produces negligible variation in the polar field and the solar cycle. However, randomness due to BMR flux distribution produces substantial effects, while the scatter in the tilt around Joy’s law produces the largest variation. Our comparative analyses suggest that the scatter of BMR tilt around Joy’s law is the major cause of variation in the solar cycle. Furthermore, our simulations also show that the magnetic field-dependent time delay of BMR emergence produces more realistic features of the magnetic cycle, consistent with observation.

中文翻译：

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由于双极磁区的不规则特性导致极地场和太阳周期的变化

观察到太阳表面倾斜双极磁区（BMR）的衰变和扩散产生了大规模的极向场，它充当环形场的种子，从而产生下一个太阳黑子周期。然而，BMR的各种特性，即倾斜度、连续出现之间的时间延迟、位置和通量都有不规则的变化。先前的研究表明，这些变化会导致极地场的变化。在这项研究中，我们首先证明我们的 3D 运动学发电机模型 STABLE 再现了表面通量输运 (SFT) 模型的稳健特征，即生成的偶极矩随 BMR 位置纬度的变化。在 SFT 和发电机模式下使用 STABLE，我们通过改变 BMR 的各个属性并根据观察结果在所有周期中保持其分布相同来进行模拟。我们发现，由于时间延迟或 BMR 纬度的分布而产生的随机性在极地场和太阳周期中产生的变化可以忽略不计。然而，由于 BMR 通量分布造成的随机性会产生很大的影响，而围绕乔伊定律的倾斜分散会产生最大的变化。我们的比较分析表明，围绕乔伊定律的 BMR 倾斜的分散是太阳周期变化的主要原因。此外，我们的模拟还表明，BMR 出现的磁场相关时间延迟产生了更真实的磁循环特征，与观察结果一致。