A very bright SAR arc: implications for extreme magnetosphere-ionosphere coupling
A very bright SAR arc: implications for extreme magnetosphere-ionosphere coupling
复制标题
非常明亮的合成孔径雷达弧：极端磁层-电离层耦合的影响
DOI：
10.5194/angeo-25-2593-2007
复制
发表时间：
2007
影响因子：
1.9
通讯作者：
M. Mendillo
中科院分区：
文献类型：
--
作者：
J. Baumgardner;J. Wroten;J. Semeter;J. Kozyra;M. Buonsanto;P. Erickson;M. Mendillo
摘要。与地磁暴期间可见的极光不同，稳定极光红弧（SAR）是中纬度地区磁层 - 电离层（M - I）直接耦合的一种亚目视表现形式。6300埃的SAR弧发射是由从环电流/等离子体层顶位置沿磁场方向的磁层能量传输进入电离层 - 热层系统所驱动的。第一个SAR弧是在太空时代初期（1956年）被观测到的，随后几十年的观测所获得的典型亮度水平和出现模式似乎与向下热传导理论相符，即受热的周围F层电子激发氧原子产生光谱纯净的发射。在极少数情况下，据报道SAR弧的亮度达到肉眼可见的水平。在此，我们报告1991年10月29日夜晚在马萨诸塞州米尔斯通山附近由四个诊断系统观测到的第一例非常明亮的SAR弧（约13千瑞利）的情况，这四个系统对亚极光区域的各个方面进行了采样：一台成像光谱仪、一台全天空相机、一台非相干散射雷达（ISR）以及一颗国防气象卫星计划（DMSP）卫星。利用ISR和DMSP数据以及MSIS中性大气模型对发射进行模拟，成功地再现了观测到的亮度水平。这有力地证实了在一次罕见的超级风暴事件期间，在内磁层最内层（L~2）中以其最极端的高层大气物理学形式存在的M - I耦合理论。异常高的亮度值似乎是由于在槽/等离子体层顶位置赤道一侧的稠密电离层等离子体罕见地受热，这与槽内较稀薄的F层更常见的受热情况形成对比。
Abstract. In contrast to the polar aurora visible during geomagnetic storms, stable auroral red (SAR) arcs offer a sub-visual manifestation of direct magnetosphere-ionosphere (M-I) coupling at midlatitudes. The SAR arc emission at 6300 A is driven by field-aligned magnetospheric energy transport from ring current/plasmapause locations into the ionosphere-thermosphere system. The first SAR arc was observed at the dawn of the space age (1956), and the typical brightness levels and occurrence patterns obtained from subsequent decades of observations appear to be consistent with the downward heat conduction theory, i.e., heated ambient F-layer electrons excite oxygen atoms to produce a spectrally pure emission. On very rare occasions, a SAR arc has been reported to be at brightness levels visible to the naked eye. Here we report on the first case of a very bright SAR arc (~13 kilo-Rayleighs) observed by four diagnostic systems that sampled various aspects of the sub-auroral domain near Millstone Hill, MA, on the night of 29 October 1991: an imaging spectrograph, an all-sky camera, an incoherent scatter radar (ISR), and a DMSP satellite. Simulations of emission using the ISR and DMSP data with the MSIS neutral atmosphere succeed in reproducing the brightness levels observed. This provides a robust confirmation of M-I coupling theory in its most extreme aeronomic form within the innermost magnetosphere (L~2) during a rare superstorm event. The unusually high brightness value appears to be due to the rare occurrence of the heating of dense ionospheric plasma just equatorward of the trough/plasmapause location, in contrast to the more typical heating of the less dense F-layer within the trough.