The Nonpotentiality of Active-Region Coronae and the Dynamics of the Photospheric Magnetic Field
The Nonpotentiality of Active-Region Coronae and the Dynamics of the Photospheric Magnetic Field
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DOI：
10.1086/430733
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发表时间：
2005-07
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影响因子：
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通讯作者：
C. Schrijver;M. DeRosa;A. Title;T. Metcalf
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文献类型：
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作者：
C. Schrijver;M. DeRosa;A. Title;T. Metcalf
太阳光球层中的磁场经常携带很强的电流，即使全球日冕结构经常类似于日光层电流片环绕的势场。为了理解这一点，我们比较了活动区日冕的踪迹EUV图像和基于95个活动区的SOHO MDI磁图的位场源表面外推。我们的结论是：(1)在过去30小时内，当一个活动区内或附近出现新的磁通，导致复杂的极性分离线时，或(2)当以4‘分辨率快速演化的相反的极性浓度接触时，整个活动区的日冕场发生显著的无位势。如果超过15%的区域通量满足这些标准，则在88%的情况下，它们正确地识别(非)活动区冠状病毒的潜力。有日冕的活动区的耀斑发生频率是近势区的2.4倍，而它们的平均X射线峰值耀斑亮度是近势区的3.3倍。我们认为，与日冕无电势相关的电流具有大约10-30小时的特征增长和衰减时间尺度。我们发现，只有当在上述时间尺度内出现复杂和动态的通量时，切变流动才能驱动增强的耀斑或日冕无位势。我们讨论了这一发现对日冕-日球层耦合模型的影响。
The magnetic field in the solar photosphere frequently carries strong electric currents, even though the global coronal configuration often resembles a potential field ringed by the heliospheric current sheet. To understand this, we compare TRACE EUV images of active-region coronae and potential-field source-surface extrapolations based on SOHO MDI magnetograms for 95 active regions. We conclude that significant nonpotentiality of the overall active-region coronal field occurs (1) when new flux has emerged within or very near a region within the last ~30 hr, resulting in complex polarity separation lines, or (2) when rapidly evolving, opposite-polarity concentrations are in contact at 4'' resolution. If these criteria are met by more than 15% of the region's flux, they correctly identify the (non) potentiality of active-region coronae in 88% of the cases. Flares are found to occur 2.4 times more frequently in active regions with nonpotential coronae than in near-potential regions, while their average X-ray peak flare brightness is 3.3 times higher. We suggest that the currents associated with coronal nonpotentiality have a characteristic growth and decay timescale of ~10-30 hr. We find that shear flows drive enhanced flaring or coronal nonpotentiality only if associated with complex and dynamic flux emergence within the above timescale. We discuss the implications of this finding for the modeling of the coronal-heliospheric coupling.