Flow bursts, breakup arc, and substorm current wedge
Flow bursts, breakup arc, and substorm current wedge
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流爆发、破碎弧和亚暴电流楔
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发表时间：
2015
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通讯作者：
G. Haerendel
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作者：
G. Haerendel
近地尾重联过程释放的能量在亚暴期间通过流爆发向偶极磁层输送。破裂弧是在气流制动和能量沉积作用下爆发到达的表现。它的结构和行为是在五个显著的空间、时间和能量特性的基础上进行定性和部分定量分析的。一个关键因素是止损层的形成。它们是离子陀螺半径宽度的薄层，其中磁场从尾部过渡到近偶极磁层构型，其中快速流动的动能转化为动能alfvsamn波的电磁能。这些流动是由流爆前段强磁剪应力的松弛引起的。在广阔的向极地扩展的分裂弧内，宽度小于10公里的明亮窄弧，本质上是阿尔夫萨奇，视觉上以不稳定的短命射线为特征，被视为停止层的痕迹。两个狭窄而高度结构化的弧线之间的间隙充满了更多的漫射辐射。这是由于流爆磁场的松弛造成的。沿着弧形向东流动与两个连续弧形之间缩小的间隙以及极光流光在午夜部分进入偶极磁层有关。停止层中的流动制动形成了多对狭窄的平衡流，不可能在亚风暴流楔形成的后面。相反，它的起源归因于高磁剪切放松，快速流动和停止层过程消退后，高β等离子体流爆发的双极化磁场施加的力，换句话说，是“垂死流爆发”。
Energy liberated by the reconnection process in the near‐Earth tail is transported via flow bursts toward the dipolar magnetosphere during substorms. The breakup arc is a manifestation of the arrival of the bursts under flow braking and energy deposition. Its structure and behavior is analyzed on the basis of five striking spatial, temporal, and energetic properties, qualitatively and in part also quantitatively. A key element is the formation of stop layers. They are thin layers, of the width of an ion gyro radius, in which the magnetic field makes a transition from tail to near‐dipolar magnetosphere configurations and in which the kinetic energy of fast flows is converted into electromagnetic energy of kinetic Alfvén waves. The flows arise from the relaxation of the strong magnetic shear stresses in the leading part of the flow bursts. The bright narrow arcs of less than 10 km width inside the broad poleward expanding breakup arc, Alfvénic in nature and visually characterized by erratic short‐lived rays, are seen as traces of the stop layers. The gaps between two narrow and highly structured arcs are filled with more diffuse emissions. They are attributed to the relaxation of the less strained magnetic field of the flow bursts. Eastward flows along the arcs are linked to the shrinking gaps between two successive arcs and the entry of auroral streamers into the dipolar magnetosphere in the midnight sector. Flow braking in the stop layers forms multiple pairs of narrow balanced currents and cannot be behind the formation of the substorm current wedge. Instead, its origin is attributed to the force exerted by the dipolarized magnetic field of the flow bursts on the high‐beta plasma, after the high magnetic shears have relaxed and the fast flows and stop layer process have subsided, in other words, to the “dying flow bursts.”