The ideal magnetohydrodynamic torus instability can drive the eruption of coronal mass ejections. The critical threshold of magnetic field strength decay for the onset of the torus instability occurs at different heights in different solar active regions, and understanding this variation could therefore improve space weather prediction. In this work, we aim to find out how the critical torus instability height evolves throughout the solar activity cycle. We study a significant subset of HMI and MDI Space-Weather HMI Active Region Patches (SHARPs and SMARPs) from 1996-2023, totalling 21584 magnetograms from 4436 unique active region patches. For each magnetogram, we compute the critical height averaged across the main polarity inversion line, the total unsigned magnetic flux and the separation between the positive and negative magnetic polarities. We find the critical height in active regions varies with the solar cycle, with higher (lower) average critical heights observed around solar maximum (minimum). We conclude this is because the critical height is proportional to the separation between opposite magnetic polarities, which in turn is proportional to the total magnetic flux in a region, and more magnetic regions with larger fluxes and larger sizes are observed at solar maximum. This result is noteworthy because, despite the higher critical heights, more CMEs are observed around solar maximum than at solar minimum.
Magnetic Decay Index Profile and Coronal Mass Ejection Speed
University of Potsdam（波茨坦大学）；George Mason University（乔治梅森大学）；Lockheed Martin Solar & Astrophysics Laboratory（洛克希德·马丁太阳与天体物理实验室）；Predictive Science, Inc.（预测科学公司）
A comparative study between a failed and a successful eruption initiated from the same polarity inversion line in AR 11387
在本文中，我们分析了2011年12月25日从NOAA AR 11387内的同一极性反转线发起的失败和成功的喷发。它们都是从剪切弧重联开始的，具有不同的喷发前条件和喷发细节：失败前，核心区的磁场具有较弱的非势性;外部场具有相似的环面不稳定临界高度，相似的局部环面稳定区，但较成功前有较大的磁通量比（低冕区和近地表区）。在失败的喷发过程中，一个较小的洛伦兹力脉冲施加在向外的喷出物上，喷出物的上升速度要慢得多。结果表明：（1）核心区的非势能较弱，洛伦兹力冲量较小，喷出物动量较小;（2）大的流量比，日冕中局部的环形稳定区提供了强约束，使喷发结构恢复到平衡态。
Helical Kink Instability in the confined Solar Eruption on 2002 May 27
通过扩展Torok & Kliem 2005和Hassanin & Kliem 2016对2002年5月~27日太阳活动区NOAA~9957的暗条爆发的参数研究，提出了一个改进的MHD模型。这里，初始通量绳平衡被选择为具有与观察到的初始细丝高度相同的小顶点高度，这意味着更真实地包含光球线束缚。该模型与先前研究中的观测结果一样接近，对于大约$4π$的初始平均磁通绳扭转，再次获得了最接近的一致性。因此，模型强烈扭动局限的太阳爆发，它假设一个扭结不稳定的磁通量绳的环面不稳定的稳定域中存在的爆发的主要加速阶段的发病，进一步证实。
Distribution of magnetic helicity and energy with height in solar atmosphere
State Key Laboratory of Solar Activity and Space Weather, National Astronomical Observatories, Chinese Academy of Sciences（中国科学院国家天文台太阳活动与空间天气国家重点实验室）；University of Chinese Academy of Sciences（中国科学院大学）
