We present a model for separator reconnection due to an isolated reconnection process. Separator reconnection is a process which occurs in the neighbourhood of a distinguished field line (the separator) connecting two null points of a magnetic field. It is, for example, important for the dynamics of magnetic flux at the dayside magnetopause and in the solar corona. We find that, above a certain threshold, such a reconnection process generates new separators which leads to a complex system of magnetic flux tubes connecting regions of previously separated flux. Our findings are consistent with the findings of large numbers of separators in numerical simulations. We discuss how to measure and interpret the reconnection rate in a configuration with multiple separators.
Magnetic reconnection occurs when new flux emerges into the corona and becomes incorporated into the existing coronal field. A new active region (AR) emerging in the vicinity of an existing AR provides a convenient laboratory in which reconnection of this kind can be quantified. We use high time-cadence 171 $Å$ data from SDO/AIA focused on new/old active region pair 11147/11149, to quantify reconnection. We identify new loops as brightenings within a strip of pixels between the regions. This strategy is premised on the assumption that the energy brightening a loop originates in magnetic reconn…
Spectroscopic Observations of Magnetic Reconnection and Chromospheric Evaporation in an X-shaped Solar Flare
我们提出了在一个非典型的X形耀斑（SOL 2014 -11- 09 T15：32）期间，由界面区域成像光谱仪（IRIS）观测到的不同位置的不同紫外光谱特性的观测结果。在这个耀斑中，出现了四条色球带，并会聚在一个X点，那里有一个分离器被锚定。在X点上方，两组非共面冠状环横向接近并在分离器处重新连接。IRIS狭缝位于X点附近，穿过一些扩口带和环。在分离器附近，Si IV 1402.77 A线表现出明显加宽的线翼，延伸到200 km/s，但线芯没有移动。这些光谱特征表明可能与分离器重连有关的双向流动的存在。而在耀斑带中，热的Fe XXI 1354.08 A谱线出现蓝移，冷的Si IV 1402.77 A，C II 1335.71 A和Mg II 2803.52 A谱线出现明显的红移，红移速度可达80 km/s，这与色球蒸发/凝结的情况相一致。
Magnetic reconnection is a fundamental process in a laboratory, magnetospheric, solar and astrophysical plasma, whereby magnetic energy is converted into heat, bulk kinetic energy and fast particle energy. Its nature in two dimensions is much better understood than in three dimensions (3D), where its character is completely different and has many diverse aspects that are currently being explored. Here we focus on the magnetohydrodynamics of 3D reconnection in the plasma environment of the solar system, especially solar flares. The theory of reconnection at null points, separators and quasi-sep…
Context. Recent observations have shown that magnetic flux cancellation occurs at the photosphere more frequently than previously thought. Aims. In order to understand the energy release by reconnection driven by flux cancellation, we previously studied a simple model of two cancelling polarities of equal flux. Here, we further develop our analysis to achieve a more general setup where the two cancelling polarities have unequal magnetic fluxes and where many new features are revealed. Methods. We carried out an analytical study of the cancellation of two magnetic fragments of unequal and oppos…
One of the major discoveries of Hinode's Extreme-ultraviolet Imaging Spectrometer (EIS) is the presence of upflows at the edges of active regions. As active regions are magnetically connected to the large-scale field of the corona, these upflows are a likely contributor to the global mass cycle in the corona. Here we examine the driving mechanism(s) of the very strong upflows with velocities in excess of 70 km/s, known as blue-wing asymmetries, observed during the eruption of a flux rope in AR 10977 (eruptive flare SOL2007-12-07T04:50). We use Hinode/EIS spectroscopic observations combined wit…
Understanding how the release of stored magnetic energy contributes to the generation of non-thermal high energy particles during solar flares is an important open problem in solar physics. Magnetic reconnection plays a fundamental role in the energy release and conversion processes taking place during flares. A common approach for investigating particle acceleration is to use test particles in fields derived from magnetohydrodynamic (MHD) simulations of reconnection. These MHD simulations use anomalous resistivities that are much larger than the Spitzer resistivity based on Coulomb collisions…
Three-dimensional (3D) magnetohydrodynamic simulations are carried out to explore magnetic reconnections in the presence of 3D magnetic nulls and quasi-separatrix layers (QSLs). The initial magnetic fields are created by superposing uniform vertical magnetic fields of two different magnitudes on a linear force-free field. The interior of the numerical box contains two 3D nulls with separatrix domes separated by a quasi-separator (or hyperbolic flux tube) with QSLs. In the first simulation, the uniform vertical field is so large that the nulls are located at low heights and the domes are separa…
We propose a new ``helicity-pumping'' method for energizing coronal equilibria that contain a magnetic flux rope (MFR) toward an eruption. We achieve this in a sequence of magnetohydrodynamics relaxations of small line-tied pulses of magnetic helicity, each of which is simulated by a suitable rescaling of the current-carrying part of the field. The whole procedure is ``magnetogram-matching'' because it involves no changes to the normal component of the field at the photospheric boundary. The method is illustrated by applying it to an observed force-free configuration whose MFR is modeled with …
Context. The recent discovery of much greater magnetic flux cancellation taking place at the photosphere than previously realised has led us in our previous works to suggest magnetic reconnection driven by flux cancellation as the cause of a wide range of dynamic phenomena, including jets of various kinds and solar atmospheric heating. Aims. Previously, the theory considered energy release at a two-dimensional current sheet. Here we develop the theory further by extending it to an axisymmetric current sheet in three dimensions without resorting to complex variable theory. Methods. We analytica…
Magnetic Reconnection in Non-Equilibrium Ionization Plasma
本文研究了日冕中含时电离和复合过程对磁重联的影响。在Petschek型稳态重联模型中，磁能量主要在慢模激波处转换。我们在磁重联结构中进行了含时电离计算。我们只计算了铁的瞬时电离，其他物种被假定为处于电离平衡。还计算了特定波长的线发射强度，以便与{ \it Hinode}或将来的其他观测结果进行比较。我们的发现如下：（1）在重联区铁主要处于非平衡电离状态;（2）用含时电离计算估算的线发射强度与电离平衡假设的结果有显著差异;（3）在电子密度小于$10^{10}$ cm $^{-3}$的情况下，含时电离的影响对电子密度敏感，（4）热传导效应减弱了含时电离效应;（5）即使考虑含时电离，辐射冷却效应也很小，可以忽略不计。
Microflares, one of small-scale solar activities, are believed to be caused by magnetic reconnection. Nevertheless, their three-dimensional (3D) magnetic structures, thermodynamic structures, and physical links to the reconnection have been unclear. In this Letter, based on high-resolution 3D radiative magnetohydrodynamic simulation of the quiet Sun spanning from the upper convection zone to the corona, we investigate 3D magnetic and thermodynamic structures of three homologous microflares. It is found that they originate from localized hot plasma embedded in the chromospheric environment at t…
We use extensive 3D resistive MHD simulations to study how large-scale current sheets will undergo fast reconnection in the high Lundquist number $S$ limit (above $\sim 10^4$), when the system is subject to different externally driven turbulence levels and the self-generated turbulence produced by 3D reconnection dynamics. We find that the normalized global reconnection rate $\sim 0.01 - 0.13$, weakly dependent on $S$. Global reconnection with the classic inflow/outflow configurations is observed, and 3D flux ropes are hierarchically formed and ejected from reconnection regions. A statistical …
This study on plasma heating considers the time-dependent ionization process during a large solar flare on September 10, 2017, observed by Hinode/EIS. The observed FeXXIV / FeXXIII ratios increase downstream of the reconnection outflow, and they are consistent with the time-dependent ionization effect at a constant electron temperature Te = 25 MK. Moreover, this study also shows that the non-thermal velocity, which can be related to the turbulent velocity, reduces significantly along the downstream of the reconnection outflow, even when considering the time-dependent ionization process.
Pulse-beam heating of deep atmospheric layers triggering their oscillations and upwards moving shocks that can modulate the reconnection in solar flares
The Dynamics of Stellar Coronae Harboring Hot-jupiters I. A Time-dependent MHD Simulation of the Interplanetary Environment in the HD 189733 Planetary System
Investigating Energetic X-Shaped Flares on the Outskirts of A Solar Active Region
典型的太阳耀斑在色球层上显示出两条准平行的明亮带状物。在它们之间的是极性反转线（PIL），其分离有源区（AR）中相反极性的集中磁通量。有趣的是，在NOAA AR 11967外围的类似位置也发生了一系列X形条带的耀斑，那里的磁通量分散，但其中三个耀斑的能量惊人。X形状，其中心与硬X射线发射重合，在UV/EUV中是相似的，这在标准耀斑模型中是不能容纳的。绘制出势场中的磁连通性，我们发现X形态由两个准分界线层的交叉决定，即，双曲线通量管（HFT），其中嵌入连接双零的分离器。这种拓扑结构不是纯粹的局部，而是受整个AR的通量和流量的调节。非线性无力场模型建议在HFT处形成电流层，其中电流耗散可以通过场对准热传导映射到X形带。这些结果突出了高频电磁场在三维磁重联中的关键作用，并对天体物理和实验室等离子体具有重要意义。
We present statistical analysis of 11,200 proton kinetic-scale current sheets (CS) observed by Parker Solar Probe during 10 days around the first perihelion. The CS thickness $λ$ is in the range from a few to 200 km with the typical value around 30 km, while current densities are in the range from 0.1 to 10\;$μ{\rm A/m^2}$ with the typical value around 0.7\;$μ{\rm A/m^2}$. These CSs are resolved thanks to magnetic field measurements at 73--290 Samples/s resolution. In terms of proton inertial length $λ_{p}$, the CS thickness $λ$ is in the range from about $0.1$ to $10λ_{p}$ with the typical va…
