SOLAR CYCLE VARIATIONS OF CORONAL NULL POINTS: IMPLICATIONS FOR THE MAGNETIC BREAKOUT MODEL OF CORONAL MASS EJECTIONS
SOLAR CYCLE VARIATIONS OF CORONAL NULL POINTS: IMPLICATIONS FOR THE MAGNETIC BREAKOUT MODEL OF CORONAL MASS EJECTIONS
复制标题
日冕零点的太阳周期变化：对日冕物质抛射磁爆发模型的影响
DOI：
10.1088/0004-637x/704/2/1021
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发表时间：
2009
期刊：
影响因子：
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通讯作者：
D. Nandy
中科院分区：
文献类型：
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作者：
G. R. Cook;D. H. Mackay;D. Nandy
本文采用磁通量输运和位场源面模型相结合的方法，研究了日冕零点和球面磁爆构型的太阳周期变化。在模拟中，在两个太阳周期内总共发现了2843个日冕零点和爆发构型。研究发现，日冕零点的数量在整个太阳周期内呈周期性变化，与通量出现率同步。在周期最大时，每天出现15-17个日冕零点的峰值。从上升阶段到下降阶段，空值的数量没有明显变化。这表明磁暴模型适用于太阳周期的两个阶段。此外，当模拟用于构造天气数据集时，如Kitt Peak提供的数据，日冕零点的数量减少了1/6。绝大多数日冕零点位于活动纬度以上，是活动区场复杂性质的结果。只有8%的日冕零点与全球偶极子有关。另一个有趣的特征是，由于位于南北半球的两极之间的跨赤道相互作用，18%的日冕零点被发现位于赤道上方。由于大多数日冕零点形成在活动纬度以上，它们的平均径向范围被发现在1.25R☉(光球层以上17.5万公里)以下的低日冕。通过考虑底层光球通量，发现71%的日冕零点是由同一半球内的两极相互作用产生的四极通量分布产生的。当将每一次自转中出现的日冕零点的数量与出现的两极子的数量进行比较时，发现了广泛的散布。日冕零点与新兴两极的比例约为1/3。总体来说，日冕零点的时空演化遵循典型的太阳蝴蝶图，并与观测到的日冕物质抛射源区位置的时间依赖性定性一致。
In this paper, we investigate the solar cycle variation of coronal null points and magnetic breakout configurations in spherical geometry, using a combination of magnetic flux transport and potential field source surface models. Within the simulations, a total of 2843 coronal null points and breakout configurations are found over two solar cycles. It is found that the number of coronal nulls present at any time varies cyclically throughout the solar cycle, in phase with the flux emergence rate. At cycle maximum, peak values of 15–17 coronal nulls per day are found. No significant variation in the number of nulls is found from the rising to the declining phase. This indicates that the magnetic breakout model is applicable throughout both phases of the solar cycle. In addition, it is shown that when the simulations are used to construct synoptic data sets, such as those produced by Kitt Peak, the number of coronal nulls drops by a factor of 1/6. The vast majority of the coronal nulls are found to lie above the active latitudes and are the result of the complex nature of the underlying active region fields. Only 8% of the coronal nulls are found to be connected to the global dipole. Another interesting feature is that 18% of coronal nulls are found to lie above the equator due to cross-equatorial interactions between bipoles lying in the northern and southern hemispheres. As the majority of coronal nulls form above active latitudes, their average radial extent is found to be in the low corona below 1.25 R☉ (175, 000 km above the photosphere). Through considering the underlying photospheric flux, it is found that 71% of coronal nulls are produced though quadrupolar flux distributions resulting from bipoles in the same hemisphere interacting. When the number of coronal nulls present in each rotation is compared to the number of bipoles emerging, a wide scatter is found. The ratio of coronal nulls to emerging bipoles is found to be approximately 1/3. Overall, the spatio-temporal evolution of coronal nulls is found to follow the typical solar butterfly diagram and is in qualitative agreement with the observed time dependence of coronal mass ejection source-region locations.