Role and origin of the poleward Alfvénic arc
Role and origin of the poleward Alfvénic arc
复制标题
极地阿尔芬弧的作用和起源
DOI：
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发表时间：
2014
期刊：
影响因子：
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通讯作者：
H. Frey
中科院分区：
文献类型：
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作者：
G. Haerendel;H. Frey
AlfvéNic弧常出现在亚风暴凸起的极地边界附近。它们是由能量分布广泛的窄电子束产生的，能量分布主要低于1keV，主要由1赫兹范围内小尺度和频率的AlfvéNic结构主导。它们也与横向离子加热有关。伴随着极地AlfvéNic弧的平衡场向电流系统揭示了其底层结构是一条数十公里宽的一次能源流入的宽广通道。相关的磁切应力驱动沿亚暴电流楔形极向一侧的流动。极冠对流在进入亚风暴凸起之前通过这个通道。小尺度电磁结构是由电离层Alfvén谐振器中的尺度破裂和多次反射的一次能量流入发展而来的。通过其平行的电场分量，这些结构有效地与电离层解耦。它们的能量含量转化为极光粒子在电离层上方的动能。选择了FAST、DE 2和CLUSTER中的一个数据集来表征Alfvénic电弧的能量和电磁性质。它在亚暴中的作用可以概括为对极帽等离子体和磁场的预调节，以便通过向极弧进入磁层。这发生在大量密度耗尽的情况下。
Alfvénic arcs are often found adjacent to the poleward border of the substorm bulge. They are created by precipitating narrow electron beams with a broad energy distribution, mainly below 1 keV, and dominated by Alfvénic structures of small scales and frequencies in the 1 Hz range. They are also associated with transverse ion heating. A balanced field‐aligned current system accompanying the poleward Alfvénic arc reveals its underlying structure being a broad channel of primary energy inflow of several tens of kilometers width. The associated magnetic shear stresses drive a flow along the poleward side of the substorm current wedge. Polar cap convection passes through this channel before entering the substorm bulge. The small‐scale electromagnetic structures are developing from the primary energy inflow by scale breaking and multiple reflections in the ionospheric Alfvén resonator. By their parallel electric field components these structures decouple effectively from the ionosphere. Their energy content is converted into kinetic energy of auroral particles in the topside ionosphere. A selected data set from FAST, DE 2, and Cluster is presented for characterizing the energetic and electromagnetic properties of the Alfvénic arc. Its function in the substorm can be summarized as a preconditioning of the polar cap plasma and magnetic field for entry into the magnetosphere through the poleward arc. This occurs under substantial density depletion.