Analysis and generation mechanism of auroral microstructure

极光的小尺度结构和动力学预计将包含与极顶电离层和磁层耦合区极光粒子产生机制有关的基本线索。基于这一观点，在本项目中，我们开发了一个计算机程序，直接从连续的视频帧使用梯度法光流算法推导出小尺度极光的速度矢量。此后，我们应用这种技术来研究各种微型/小型极光的特征;我们还对挪威特罗姆瑟的小尺度极光进行了EISCAT雷达和光学成像仪的同步观测，为了弄清小尺度极光附近的等离子体和电场的情况。以下特征在本研究中变得明显。1.形成卷曲的离散弧的厚度最薄，约为100 m.在旋度形成过程中，出现了几个100米/秒的逆时针快速运动.在闪烁的极光中，小尺度（2- 3 km）结构叠加在10- 20 km的中尺度结构上.强极光弧两侧（10公里尺度）离子温度升高.黑极光区的电子密度降低到背景漫射极光区的30-50%，但仍远高于无极光区的电子密度，这些结果已在几次科学会议上发表，目前正在准备发表。在EISCAT活动中获得的光学图像也用于名古屋大学的硕士论文工作。

Small-scale structures and dynamics of aurora are expected to contain essential clues relevant to the generation mechanisms of auroral particles in the coupling region of the topside polar ionosphere and the magnetosphere. Based on this perspective, in this project we have developed a computer program to derive the velocity vector of small-scale auroras directly from the sequential video frames using the gradient method optical flow algorism. We thereafter applied this technique to investigate the characteristics of a variety of micro/small-scale auroras; curls, flickering and black auroras, so on. It is confirmed that this method is quite useful to deduce and describe auroral dynamics, except in the case that the auroral intensity changes so rapidly.We also made simultaneous EISCAT radar and optical imager observations for small-scale auroras in Tromso, Norway, in order to clarify the condition of plasma and electric field in the vicinity of small-scale auroras. The following feature became evident in this study.1. The thickness of a discrete arc which forms into a curl is the thinnest, 〜100m approximately.2. The anti-clockwise fast motion with several 100m/sec is apparent during a curl formation.3. A small-scale(2-3km) structure is superposed in the 10-20km medium-scale structure in a flickering aurora.4. The ion temperature is elevated at both side regions(10km scale) of an intensive auroral arc.5. The electron density in a black aurora decreases to 30-50% level of the background diffuse aurora, but still keeps much higher than that of no auroral emission region.These results have been presented in several science meetings and are now in preparation for publication. The optical images acquired in the EISCAT campaign were also used in the work for master's theses at Nagoya University.