Department of Physics and Astronomy, University of Leicester, Leicester, UK.
Department of Physics and Astronomy, University of Leicester, Leicester, UK. Birkeland Centre for Space Sciences, University of Bergen, Bergen, Norway.
Science. 2014 Dec 19;346(6216):1506-10. doi: 10.1126/science.1257377.
The structure of Earth's magnetosphere is poorly understood when the interplanetary magnetic field is northward. Under this condition, uncharacteristically energetic plasma is observed in the magnetotail lobes, which is not expected in the textbook model of the magnetosphere. Using satellite observations, we show that these lobe plasma signatures occur on high-latitude magnetic field lines that have been closed by the fundamental plasma process of magnetic reconnection. Previously, it has been suggested that closed flux can become trapped in the lobe and that this plasma-trapping process could explain another poorly understood phenomenon: the presence of auroras at extremely high latitudes, called transpolar arcs. Observations of the aurora at the same time as the lobe plasma signatures reveal the presence of a transpolar arc. The excellent correspondence between the transpolar arc and the trapped closed flux at high altitudes provides very strong evidence of the trapping mechanism as the cause of transpolar arcs.
当行星际磁场为北向时，地球磁层的结构很难理解。在这种情况下，在磁尾瓣中观测到异常高能的等离子体，这与磁层的教科书模型所预期的不同。利用卫星观测，我们表明这些瓣等离子体特征发生在高纬磁场线上，这些磁场线已经通过基本的等离子体过程——磁重联而闭合。此前，有人提出，闭合磁通可以被困在瓣中，而这种等离子体捕获过程可以解释另一个难以理解的现象：极区极光的存在，称为跨极弧。在观测瓣等离子体特征的同时，也观测到了极光。在高海拔地区，跨极弧与被困的闭合磁通之间存在极好的对应关系，这为捕获机制是跨极弧形成的原因提供了非常有力的证据。
