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Analysis and generation mechanism of auroral microstructure

极光微结构分析及生成机制

基本信息

批准号：
14540418
负责人：
MIYAOKA Hiroshi
金额：
$ 1.92万
依托单位：
National Institute of Polar Research
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2002
资助国家：
日本
起止时间：
2002 至 2004
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-14540418/
关键词：
aurora small-scale structure electric field EISCAT radar optical-flow

项目摘要

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.

极光的小尺度结构和动力学预计将包含与极光粒子在顶部极地电离层和磁层耦合区域的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，利用梯度法光流算法从连续的视频帧中直接推导出小尺度极光的速度矢量。此后，我们应用这一技术研究了各种微/小尺度极光的特征：卷曲、闪烁和黑色极光等。我们还对挪威特罗姆索的小尺度极光进行了EISCAT雷达和光学成像仪的同步观测，以弄清小尺度极光附近的等离子体和电场条件。在这项研究中，以下特征变得明显。形成卷曲的离散弧线的厚度是最薄的，约为100米。在旋涡形成过程中，出现了几个100m/s的逆时针快速运动。在闪烁的极光中，一个小尺度(2-3公里)构造叠加在10-20公里的中等尺度构造中。在一个密集极光弧线的两侧区域(10公里尺度)，离子温度升高。黑色极光中的电子密度下降到背景漫射极光的30%-50%水平，但仍然比没有极光发射区的电子密度高得多。这些结果已经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被用于名古屋大学硕士论文的工作。