This work examines the relation between the fractal properties of the photospheric magnetic patterns and those of the coronal magnetic fields in solar active regions.Our results show no correlation between the fractal dimensions of the observed 2d photospheric structures and the extrapolated unstable volumes in the corona, when nonlinear force-free extrapolation is used. This result is independent of efforts to (1) bring the photospheric magnetic fields closer to a nonlinear force-free equilibrium and (2) omit the lower part of the modeled magnetic field volume that is almost completely filled by unstable volumes. A significant correlation between the fractal dimensions of the photospheric and coronal magnetic features is only observed at the zero level (lower limit) of approximation of a current-free (potential) magnetic field extrapolation. We conclude that the complicated transition from photospheric non-force-free fields to coronal force-free ones hampers any direct correlation between the fractal dimensions of the 2d photospheric patterns and their 3d counterparts in the corona at the nonlinear force-free limit.
Coronal Non-Thermal and Doppler Plasma Flows Driven by Photospheric Flux in 28 Active Regions
University College London, Mullard Space Science Laboratory(伦敦大学学院,穆拉德空间科学实验室);University of Vienna, Institute of Astrophysics(维也纳大学,天体物理研究所);Computational Physics, Inc.(计算物理公司);Space Science Division, Naval Research Laboratory(海军研究实验室空间科学部);NASA Goddard Space Flight Center, Solar Physics Laboratory, Heliophysics Science Division(美国国家航空航天局戈达德太空飞行中心,太阳物理学实验室,日球物理科学部);Department of Mathematics, Physics and Electrical Engineering, Northumbria University(诺森比亚大学数学、物理与电气工程系);INAF Osservatorio Astronomico di Roma(意大利国家天体物理研究所罗马天文台)
The Magnetic Field of Active Region 11158 During the 2011 February 12-17 Flares : Differences between Photospheric Extrapolation and Coronal Forward-Fitting Methods
Magnetic flux ropes are bundles of twisted magnetic field enveloping a central axis. They harbor free magnetic energy and can be progenitors of coronal mass ejections (CMEs), but identifying flux ropes on the Sun can be challenging. One of the key coronal observables that has been shown to indicate the presence of a flux rope is a peculiar bright coronal structure called a sigmoid. In this work, we show Hinode EUV Imaging Spectrometer (EIS) observations of sigmoidal active region 10977. We analyze the coronal plasma composition in the active region and its evolution as the sigmoid (flux rope) …
It is well known that magnetic fields dominate the dynamics in the solar corona, and new generation of numerical modelling of the evolution of coronal magnetic fields, as featured with boundary conditions driven directly by observation data, are being developed. This paper describes a new approach of data-driven magnetohydrodynamic (MHD) simulation of solar active region (AR) magnetic field evolution, which is for the first time that a data-driven full-MHD model utilizes directly the photospheric velocity field from DAVE4VM. We constructed a well-established MHD equilibrium based on a single v…
Context: Many previous studies have shown that the magnetic precursor of a coronal mass ejection (CME) takes the form of a magnetic flux rope, and a subset of them have become known as `hot flux ropes' due to their emission signatures in $\sim$10 MK plasma. Aims: We seek to identify the processes by which these hot flux ropes form, with a view of developing our understanding of CMEs and thereby improving space weather forecasts. Methods: Extreme-ultraviolet observations were used to identify five pre-eruptive hot flux ropes in the solar corona and study how they evolved. Confined flares were o…
Preferential Appearance of H$α$ Moreton Waves along Photospheric Magnetic Network Boundaries
School of Astronomy and Space Science, Nanjing University(南京大学天文与空间科学学院);Key Laboratory for Modern Astronomy and Astrophysics, Nanjing University(南京大学现代天文与天体物理重点实验室);State Key Laboratory of Lunar and Planetary Sciences, Macau University of Science and Technology(澳门科技大学月球与行星科学国家重点实验室)
Elemental abundances in the solar corona are known to be different from those observed in the solar photosphere. The ratio of coronal to photospheric abundance shows a dependence on the first ionisation potential (FIP) of the element. We estimate FIP bias from direct measurements of elemental abundances from soft X-ray spectra using data from multiple space missions covering a range of solar activity levels. This comprehensive analysis shows clear evidence for a decrease in FIP bias around maximum intensity of the X-ray flare with coronal abundances briefly tending to photospheric values and a…
First Flare-related Rapid Change of Photospheric Magnetic Field Observed by Solar Dynamics Observatory
光球磁场不仅在积累自由能和触发太阳爆发方面起着重要作用,而且被观测到会随着日冕瞬变引起的日冕磁场重构而发生快速而持久的变化。新发射的太阳动力学天文台(SDO)上的日震和磁成像仪(HMI)以一贯的高分辨率和高节奏产生无视全磁盘矢量磁图,这最终使得对这一重要的反反应过程进行明确和全面的研究成为可能。在这项研究中,我们提出了一个近盘中心,GOES级X2.2耀斑发生在NOAA AR 11158在2011年2月15日使用的磁场测量HMI。我们获得了第一个坚实的证据,增强横向磁场在耀斑磁极性反转线(PIL)的幅度为70%。这种快速和不可逆的场演化与耀斑的发生有明确的联系,增强区位于两个色球耀斑带之间。SDO观测到的另外两次主要耀斑事件也有类似的发现。这些结果强有力地证实了我们先前的建议,光球磁场附近的PIL必须变得更加水平后爆发。随后将进行深入研究,进一步将光球磁场变化与日冕物质抛射的动态联系起来,届时将进行全斯托克斯反演,以生成准确的磁场矢量。
Validating Coronal Magnetic Field Models Using Gaussian Separation
Sydney Institute for Astronomy, School of Physics, The University of Sydney(悉尼大学);University of Wisconsin-Green Bay(威斯康星大学格林贝分校);W.W. Hansen Experimental Physics Laboratory, Stanford University(斯坦福大学);The University of Newcastle(纽卡斯尔大学)
Rapid Changes of Photospheric Magnetic Field after Tether-Cutting Reconnection and Magnetic Implosion
光球磁场的快速、不可逆变化被认为是太阳耀斑过程的一个重要因素。这封信报告了2011年2月13日NOAA AR 11158 M6.6耀斑期间磁场的快速变化,我们从日震和磁成像仪的矢量磁图中发现了12分钟的节奏。在非线性无力场(NLFFF)假设下,利用太阳耀斑极大值前后~-5.5,-1.5,1.5和4小时的高分辨率磁象图重建三维日冕磁场。紫外和硬X射线图像也被用来阐明磁场的演变和能量释放。快速变化主要由HMI在位于磁S形中心的紧凑区域中检测到,其中平均水平场强表现出28%的显著增加。该区域位于色球层中的初始强UV和硬X射线源之间,根据NLFFF模型,它们与S形的中央脚是同空间的。NLFFF模型进一步表明,强日冕电流集中在该地区的正上方,更有趣的是,日冕电流系统在S型爆发后经历了明显的向下崩溃。这些结果进行了讨论,有利于系绳切割重联产生的耀斑和随后的内爆的日冕领域所造成的能量释放。
Photospheric horizontal magnetic field decrease preceding a major solar eruption
Planetary Environmental and Astrobiological Research Laboratory (PEARL), School of Atmospheric Sciences, Sun Yat-sen University(中山大学大气科学学院行星环境与天体生物学研究实验室);CAS center for Excellence in Comparative Planetology(中国科学院比较行星学卓越中心);Key Laboratory of Tropical Atmosphere-Ocean System, Sun Yat-sen University, Ministry of Education(中山大学热带海洋-大气系统教育部重点实验室)
The subject of this study is oscillations in the lower atmosphere in coronal-hole regions, where the conditions are favorable for propagation between the atmospheric layers. Based on spectroscopic observations in photospheric and chromospheric lines, we analysed the features of the oscillations that show signs of propagation between layers of the solar atmosphere. Using the cross-spectrum wavelet algorithm, we found that both chromospheric and photospheric signals under coronal holes share a range of significant oscillations of periods around five minutes, while the signals outside of coronal …
Magnetic helicity (MH) is a measure of twist and shear of magnetic field. MH is injected in the active region (AR) corona through photospheric footpoint motions causing twisted and sheared magnetic fields. From the conservation property of the helicity, it was conjectured that an already twisted flux rope (FR) with continuous injection of MH inevitably erupts to remove the excess accumulated coronal helicity. Therefore, understanding the nature and evolution of the photospheric helicity flux transfer is crucial to reveal the intensity of the flare/CME activity. Using the time-sequence vector-m…