ON THE STRUCTURE AND EVOLUTION OF COMPLEXITY IN SIGMOIDS: A FLUX EMERGENCE MODEL
ON THE STRUCTURE AND EVOLUTION OF COMPLEXITY IN SIGMOIDS: A FLUX EMERGENCE MODEL
复制标题
DOI：
10.1088/0004-637x/691/2/1276
复制
发表时间：
2009-02-01
影响因子：
4.9
通讯作者：
Deluca, E.
中科院分区：
文献类型：
--
作者：
Archontis, V.;Hood, A. W.;Deluca, E.
S形是一种正S形或反S形的结构，通常在日冕的软X射线发射中观察到。据认为，在活动区出现的S形是喷发活动的一个重要因素。由于S形团与诸如耀斑和日冕物质抛射（CME）等动力学现象的联系，使得对S形团的研究具有重要意义。最近的观测，日冕S形，获得了X射线望远镜（XRT）上的日之出，显示了形成和喷发阶段的高空间分辨率。这些观察结果显示，S形的拓扑结构是复杂的：它由许多不同方向的环组成，它们共同形成两个相对的J形束或一个整体的S形结构。在过去的几年里，已经提出了一系列的理论和数值模型来解释S形曲线的性质，但没有解释S形曲线中的上述复杂性是如何建立的。在本文中，我们提出了一个通量出现模型，导致形成的S形，其结构和复杂性的演变是在很好的定性与最近的观察。在实验的初始状态，一个扭曲的通量管被放置在光球层下面。沿管轴沿着的密度差使系统在中间漂浮，当它向外大气层上升时，它采用O形。在系统演化过程中，在光秃斑（BPs）处与光球接触的扩展磁力线形成两个分界面，在分界面处耗散增强，形成电流片。最初，每个BP分面都具有类似J的形状。每一个J都由不同形状和不同相对方向的重新连接的场线组成。新兴的通量管的进一步动力学演化的结果在许多网站的出现，类似于旋转不连续。因此，在上升的磁化体积内形成额外的电流层，增加了系统的复杂性。沿着这些层重新连接的场线沿着形成整体S形结构。重连过程继续发生，导致在乙状结肠中间形成另一个电流集中，在那里发生耀斑发作。这种中央增亮伴随着从S形中央区域喷发出的通量绳，以及在当前结构下方出现的“耀斑后”环。
Sigmoids are structures with a forward or inverse S-shape, generally observed in the solar corona in soft X-ray emission. It is believed that the appearance of a sigmoid in an active region is an important factor in eruptive activity. The association of sigmoids with dynamic phenomena such as flares and coronal mass ejections (CMEs) make the study of sigmoids important. Recent observations of a coronal sigmoid, obtained with the X-Ray Telescope (XRT) on board Hinode, showed the formation and eruption phase with high spatial resolution. These observations revealed that the topological structure of the sigmoid is complex: it consists of many differently oriented loops that all together form two opposite J-like bundles or an overall S-shaped structure. A series of theoretical and numerical models have been proposed, over the past years, to explain the nature of sigmoids but there is no explanation on how the aforementioned complexity in sigmoids is built up. In this paper, we present a flux emergence model that leads to the formation of a sigmoid, whose structure and evolution of complexity are in good qualitative agreement with the recent observations. For the initial state of the experiment a twisted flux tube is placed below the photosphere. A density deficit along the axis of the tube makes the system buoyant in the middle and it adopts an O-shape as it rises toward the outer atmosphere. During the evolution of the system, expanding field lines that touch the photosphere at bald-patches (BPs) form two seperatrix surfaces where dissipation is enhanced and current sheets are formed. Originally, each of the BP seperatrix surfaces has a J-like shape. Each one of the J's consist of reconnected field lines with different shapes and different relative orientation. The further dynamical evolution of the emerging flux tube results in the occurrence of many sites that resemble rotational discontinuities. Thus, additional current layers are formed inside the rising magnetized volume increasing the complexity of the system. The reconnected field lines along these layers form an overall S-shaped structure. The reconnection process continues to occur leading to the formation of another current concentration in the middle of the sigmoid where a flaring episode occurs. This central brightening is accompanied by the eruption of a flux rope from the central area of the sigmoid and the appearance of "post-flare" loops underneath the current structure.