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Numerical simulations of sunspot rotation driven by magnetic flux emergence

机译:磁通出现驱动黑子旋转的数值模拟

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摘要

Magnetic flux continually emerges from the Sun, rising through the solar interior, emerging at the photosphere in the form of sunspots and expanding into the atmosphere. Observations of sunspot rotations have been reported for over a century and are often accompanied by solar eruptions and flaring activity. In this thesis, we present 3D numerical simulations of the emergence of twisted flux tubes from the uppermost layers of the solar interior, examining the rotational movements of sunspots in the photospheric plane. The basic experiment introduces the mechanism and characteristics of sunspot rotation by a clear calculation of rotation angle, vorticity, magnetic helicity and energy, whereby we find an untwisting of the interior portion of the field, accompanied by an injection of twist into the atmospheric field. We extend this model by altering the initial field strength and twist of the sub-photospheric tube. This comparison reveals the rotation angle, helicity and current show a direct dependence on field strength. An increase in field strength increases the rotation angle, the length of fieldlines extending into the atmosphere, and the magnetic energy transported to the atmosphere. The fieldline length is crucial as we predict the twist per unit lengthudequilibrates to a lower value on longer fieldlines, and hence possesses a larger rotation angle. No such direct dependence is found when varying the twist but there is a clear ordering in rotation angle, helicity, and energy, with more highly twisted tubes undergoing larger rotation angles. We believe the final angle of rotation is reached when the system achieves a constant degree of twist along the length of fieldlines. By extrapolating the size of the modelled active region, we find rotation angles and rates comparable with those observed. In addition, we explore sunspot rotation caused by sub-photospheric velocities twisting theudfootpoints of flux tubes.
机译:磁通量不断从太阳中散发出来,穿过太阳内部上升,并以黑子的形式出现在光球中并扩展到大气中。关于太阳黑子旋转的观察已经有一个多世纪的报道了,通常伴随着太阳爆发和爆发活动。在这篇论文中,我们提出了来自太阳内部最上层的扭曲通量管出现的3D数值模拟,研究了太阳黑子在光球面上的旋转运动。基本实验通过清楚地计算旋转角度,涡度,磁螺旋和能量,介绍了黑子旋转的机制和特征,从而我们发现了磁场内部的扭曲,并伴随着向大气场的扭曲注入。我们通过改变初始光强和亚光球管的扭曲来扩展该模型。这种比较表明,旋转角度,螺旋度和电流都直接取决于场强。磁场强度的增加会增加旋转角度,磁场线延伸到大气中的长度以及传输到大气中的磁能。场线长度至关重要,因为我们预测在较长的场线上单位长度的扭曲不平衡到较低的值,因此具有较大的旋转角度。改变扭曲度时,没有发现这种直接相关性,但是旋转角,螺旋度和能量有明确的顺序,扭曲度更高的管子会经历更大的旋转角。我们相信,当系统沿着磁力线的长度达到恒定的扭曲程度时,就可以达到最终的旋转角度。通过外推建模的活动区域的大小,我们发现旋转角和旋转速率与观察到的旋转角和旋转速率相当。此外,我们研究了由亚光圈速度扭曲通量管的 udfootpoints引起的黑子旋转。

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    Sturrock Zoe;

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  • 年度 2017
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