Global characteristics of field-aligned acceleration processes associated with auroral arcs
Global characteristics of field-aligned acceleration processes associated with auroral arcs
复制标题
与极光弧相关的场对准加速过程的全局特征
DOI：
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发表时间：
1991
期刊：
影响因子：
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通讯作者：
H. Fukunishi
中科院分区：
文献类型：
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作者：
K. Shiokawa;H. Fukunishi
为了研究与极光弧相关的场向加速过程的全球特征，我们分析了DMSP-F6和-F7卫星获得的粒子和极光图像数据。利用观测到的电子通量和双流电子输运代码计算了5577-A、6300-A和N2 （1PG）的极光发射强度，表明沉淀电子的通量足以产生可见的极光弧。然后，通过将加速的麦克斯韦分布函数拟合到观测到的电子能谱上，并通过评估加速过程中电子加热的影响，估计了磁层高度电子通量的密度和热能。我们得到了磁场向电位差、加速期间磁层电子密度和热能、电子升温速率以及磁场安静期和活动期极光发射强度的全球分布。磁场向电位差随磁层电子密度和绝热场向电导率的减小而增大，表明磁层-电离层电流电路存在恒流发生器。日侧弧的磁层源电子具有密度大、热能低的特点，特别是在安静期。在低纬度地区观测到的加速电子沉淀事件与LLBL有关，而在高纬度地区观测到的加速电子沉淀事件与等离子体地幔有关。在静息期，后一事件的区域扩展到高纬度区域，与等离子体地幔扩展到磁层瓣区有关。在磁层源区显示出低电子密度和高热能量的夜侧事件似乎起源于等离子体片区。早晨的副事件是高密度事件和低密度事件的混合。我们认为前一种事件的源在地幔或等离子体地幔中，后一种事件的源在扩展到尾翼区域的等离子体片中。磁层源电子在不同磁地方时和磁纬度下的这些不同特征似乎导致了全球尺度上极光弧的变化。
To study the global characteristics of field-aligned acceleration processes associated with auroral arcs, we have analyzed the particle and aurora image data obtained from the DMSP-F6 and -F7 satellites. The intensities of auroral emissions for 5577-A, 6300-A and N2 (1PG) have been calculated using the observed electron fluxes and the two-stream electron transport code to show that the fluxes of precipitating electrons are sufficient to produce visible auroral arcs. Then, the density and thermal energy of these electron fluxes at magnetospheric altitude have been estimated by fitting the accelerated Maxwellian distribution function to the observed electron energy spectra and by evaluating the effect of electron heating during the acceleration. We have obtained global distributions of the field-aligned potential difference, magnetospheric electron density and thermal energy, electron heating rate during the acceleration and auroral emission intensities for magnetic quiet and active periods, respectively. It is found that the field-aligned potential difference increases as magnetospheric electron density and adiabatic field-aligned conductivity decrease, suggesting the constant-current generator for the magnetosphere-ionosphere current circuit. The magnetospheric source electrons of dayside arcs are characterized by high density and low thermal energy, particularly in the quiet period. It is suggested that accelerated electron precipitation events observed on the lower latitude side of the cusp region are connected to the LLBL, while those observed on the higher latitude side of the cusp region are connected to the plasma mantle. In the quiet period, the region of latter events expands to higher latitude region associated with the expansion of the plasma mantle into the magnetospheric lobe region. The nightside events which show low electron density and high thermal energy at the magnetospheric source region appear to have originated from the plasma sheet region. The morning side events are a mixture of high density events and low density events. We consider that the former events have a source in the LLBL or the plasma mantle, while the latter events have a source in the plasma sheet which expands to the tail flank region. These different characteristics of magnetospheric source electrons for different magnetic local time and magnetic latitude seem to produce the variety of auroral arcs on global scale.