夜间极光弧中小尺度结构的观测与形成机制研究

Auroral arc is one of the most active topics in the field of aurora. Presently, the detailed physical mechanisms giving rise to its characteristics are to a large extent still poorly known. The latest investigations suggested that electrodynamics of the arc can exhibit also 2D features (Amm et al.,2011; Marghitu et al., 2011). This finding is an important breakthrough in the understanding about the arc, which has been widely-accepted as 1D model for a long time period. However, the specific physical processes are not clear. We propose that contribution from medium/small scale structures of precipitation particles related to the arc are important during the processes. In this project, therefore, optical intensity of digital All-Sky Camera and auroral absorption images are combined to produce high temporal/spatial resolution maps of characteristic energy of precipitating particles during night time. With help of these energy maps and auroral optical observations, medium/small scale structures and their evolution, as well as distribution of related precipitation particles are planned to be investigated. On this basis, thier role during the processes of polar ionospheric current closure will be discussed. Our aim is to uncover the formation mechanisms of these medium/small scale structures, by means of identifying their relationship with previous theories. Results of this project are likely to revise our understanding about physical precesses of the arc, being of high value to shedding more light on the complex M-I-T coupling.

极光弧是极光研究中的一个热点。目前，我们对其背后详细物理机制的理解还很贫乏。最近的研究发现：夜间极光弧电动力学过程表现出显著的二维特征（Amm et al.,2011; Marghitu et al., 2011）。这一发现突破了长期以来广为接受的一维理论模型，但其确切的物理过程和机制还未被阐明。我们推测：极光弧沉降粒子的中小尺度空间分布对此有重要贡献。为此，本项目联合地面极光全天空照相和宇宙噪声成像仪，实现对夜间极区沉降粒子能量特征参数的高时空分辨观测；探寻极光弧内沉降粒子特征能量空间分布和中小尺度立体结构的演化特征。在此基础上，探讨极光弧中小尺度结构在极区电离层电流闭合过程中的作用；辨明其与现有形成理论间的关联,揭示其形成机制。项目研究工作有望更新我们对极光弧物理过程的理解，对深入认识磁层-电离层-热层复杂耦合过程具有重要意义。

极光弧是磁层-电离层-热层耦合过程中的一个重要现象，是极光研究中的一个热点。本项目联合地面极光全天空照相和宇宙噪声成像仪，实现了夜间极区沉降粒子能量特征参数的高时空分辨图像获取方法，为从沉降粒子能量的角度对夜间极光弧中小尺度结构开展观测分析提供了重要的技术手段；利用地面全天空极光观测数据，对极光弧激发特性、极光弧走向和倾角进行了详尽分析研究，发现IMF By对极光强度有显著的控制作用；极光弧走向与上行的场向电流分布关系密切。利用DMSP卫星，对比分析了太阳活动高、低年期间高纬顶部向阳侧电离层离子上行随地磁活动水平的变化特征，发现向阳侧顶部电离层似乎存在两个效率相当的上行区域，一个位于极尖/极隙去纬度附近，离子沿开放磁力线，进入磁尾等离子体片；另一个位于晨侧亚极光区附近，离子沿闭合磁力线，进入向阳侧到了中层边界层；利用2009-2011年EISCAT/ESR雷达场向观测数据，统计研究了低太阳活动期间极区E层占优电离层（ELDI）事件的发生规律及其主要特征。研究发现极区ELDI表现出明显的季节变化特征：在冬季和早春发生率较高；而且表现出与之前无线电掩星观测结果不一致的日变化特征。.项目共发表论文11篇，其中SCI论文10篇，均标注基金资助；资助20余人次参加学术会议，其中，国际学术会议2人次；邀请国外专家3人次来校交流讲学。项目研究工作有望更新我们对极光弧物理过程的理解，对深入认识磁层-电离层-热层复杂耦合过程具有重要意义。