FAST observations of upward accelerated electron beams and the downward field-aligned current region
FAST observations of upward accelerated electron beams and the downward field-aligned current region
复制标题
向上加速电子束和向下场对准电流区域的 FAST 观测
DOI：
10.1029/gm118p0173
复制
发表时间：
2013
期刊：
影响因子：
--
通讯作者：
W. Peria
中科院分区：
文献类型：
--
作者：
R. Elphic;J. Bonnell;R. Strangeway;C. Carlson;M. Temerin;J. Mcfadden;R. Ergun;W. Peria
极光过程是磁层和电离层之间的能量和动量交换以及由此产生的电流系统的结果。在极光带的向上场向电流（FAC）区域中的场向电位降在面对相反的镜像力时保持所需的电流密度。但是，场取向的电位降也发生在向下的电流区域，并导致向上的加速电子束。我们使用FAST研究了向上加速电子随高度、磁场当地时间和季节的变化。通过选择近地点在赤道上方的轨道，南北半球在高度覆盖范围上的差异在很大程度上被消除了。在夏至附近的一段时间内，在夏季极光带的FAST高度上没有观察到电子束，而在冬季半球，71%的交叉点有上行光束，这是一个明显的季节效应。在春分间隔期间，半球之间的分布更加平衡，但总体发生率低于冬至期间（约46%）。有一个明显的趋势，上行加速电子束发生在FAST高度最大时，偶极子倾斜的地方，在夜侧电离层，在那里的背景电离层密度最低的磁力线脚点深。换句话说，随着电离层密度的降低，潜在的结构倾向于移动到较低的高度。
Auroral processes result from the exchange of energy and momentum between the magnetosphere and ionosphere, and the current systems arising from this exchange. Field-aligned potential drops in the upward field-aligned current (FAC) region of the auroral zone maintain a required current density in the face of opposing mirror forces. But field-aligned potential drops occur in downward current regions as well, and result in upgoing accelerated electron beams. We investigate the occurrence of upward accelerated electrons with altitude, magnetic local time and season using FAST. By choosing orbits having perigee over the equator, northern-southern hemisphere differences in altitude coverage are largely removed. For an interval near solstice, no electron beams were observed over the summer auroral zone at FAST altitudes, while over the winter hemisphere, 71% of the crossings had upgoing beams, a clear seasonal effect. During the equinox interval the distribution between hemispheres was much more balanced, but the overall occurrence was less (∼46%) than during winter solstice. There is a clear tendency for upgoing accelerated electron beam occurrence at FAST altitudes to maximize when dipole tilt places the field line footpoint deep in the nightside ionosphere, where background ionospheric density is lowest. In other words, as ionospheric density decreases, the potential structure tends to move to lower altitudes.