Are the Brightest Coronal Loops Always Rooted in Mixed-polarity Magnetic Flux?
Are the Brightest Coronal Loops Always Rooted in Mixed-polarity Magnetic Flux?
复制标题
DOI：
10.3847/1538-4357/abd176
复制
发表时间：
2021-02
期刊：
影响因子：
--
通讯作者：
S. Tiwari;Caroline L. Evans;N. Panesar;A. Prasad;R. Moore
中科院分区：
文献类型：
--
作者：
S. Tiwari;Caroline L. Evans;N. Panesar;A. Prasad;R. Moore
最近的一项研究表明，活动区(AR)日冕环光球脚的对流自由和磁场强度一起可以在其中产生或熄灭加热。其他研究强调，环脚处的磁通量抵消可能会导致环路中的加热。我们使用大气成像组件/太阳动力学天文台(SDO)的极端紫外线图像和日震和磁成像仪(HMI/SDO)的视线(LOS)磁图，跟踪双极AR的24小时电影，以检查23个最亮日冕环脚处的磁极。我们得到了Fe xviii发射(HOT-94)图像(使用Warren等人。方法)选择最热/最亮的环路，并通过非无力场外推确定它们的脚点位置。从LOS磁图上位于每个环足中心的6“×6”盒中，我们发现∼40%的环路具有单极磁通，∼60%的环路至少有一只脚处于混极磁通。具有双脚单极的环路平均寿命比具有混极脚点磁通的环路短15%，但它们的峰值强度平均值相同。在大多数环路中，至少一英尺处存在混合极性的磁通，这表明足点的磁通抵消可能驱动了大部分加热。但∼40%的线圈中没有混合极性的磁通(达到人机界面的检测极限)，这表明磁通抵消可能不是驱动日冕线圈加热的必要因素--磁对流和环脚两端的磁场强度可能会驱动大部分加热，即使在线圈脚呈现混合极性磁通量的情况下也是如此。
A recent study demonstrated that freedom of convection and strength of magnetic field in the photospheric feet of active-region (AR) coronal loops, together, can engender or quench heating in them. Other studies stress that magnetic flux cancellation at the loop-feet potentially drives heating in loops. We follow 24 hr movies of a bipolar AR, using extreme ultraviolet images from the Atmospheric Imaging Assembly/Solar Dynamics Observatory (SDO) and line-of-sight (LOS) magnetograms from the Helioseismic and Magnetic Imager (HMI)/SDO, to examine magnetic polarities at the feet of 23 of the brightest coronal loops. We derived Fe xviii emission (hot-94) images (using the Warren et al. method) to select the hottest/brightest loops, and confirm their footpoint locations via non-force-free field extrapolations. From 6″ × 6″ boxes centered at each loop foot in LOS magnetograms we find that ∼40% of the loops have both feet in unipolar flux, and ∼60% of the loops have at least one foot in mixed-polarity flux. The loops with both feet unipolar are ∼15% shorter lived on average than the loops having mixed-polarity foot-point flux, but their peak-intensity averages are equal. The presence of mixed-polarity magnetic flux in at least one foot in the majority of the loops suggests that flux cancellation at the footpoints may drive most of the heating. But the absence of mixed-polarity magnetic flux (to the detection limit of HMI) in ∼40% of the loops suggests that flux cancellation may not be necessary to drive heating in coronal loops—magnetoconvection and field strength at both loop feet possibly drive much of the heating, even in the cases where a loop foot presents mixed-polarity magnetic flux.