小尺度极光弧的物理特征及产生机制研究

Arc aurora is the most common auroral type, whose spatial scale is observed to extend from 100s of kilometers down to several 10s of meters. The research on small-scale auroral arcs is very important to understand the auroral acceleration mechanism and know the cross-scale coupling in magnetosphere-ionosphere system. Limited to the observational techniques, the observational study on small-scale auroral arcs is far from enough at present, unsolved issues that need observations to be confirmed include that: if the spectrum of auroral arcs widths is continuous, what are the relationships of the generation of small-scale auroral arcs with the diffuse aurora, the medium/large-scale auroral arcs, and other space physical parameters, etc. An imaging system for small-scale auroral research was installed at Chinese Zhongshan Station, Antarctica in 2009 and it has been continuously working up to now. Based on the observations obtained from the system in these years, we will make a systematic study on small-scale auroral arcs in this project by using image processing and pattern recognition technology. The research contents include 1) making an automatic recognition to auroral arc events, calculating the widths of auroral arcs and determining their distribution is continuous or discrete; 2) studying the correlation of small scale auroral arcs with diffuse aurora and medium/large scale auroral arcs; 3) with the simultaneous observations from ground, radar and satellite, analyzing the relationships of small-scale auroral arcs with MLT, geomagnetic activities and ionosphere properties; 4) combing the current theories about the generation of auroral arcs, discuss the possible generation mechanisms of small-scale auroral arcs and promote their research to a new level.

极光弧是最常见的一种极光形态，其空间尺度小至几十米，大至数百千米。小尺度极光弧研究对理解极光粒子加速机制及磁层-电离层中的跨尺度耦合具有重要意义。受观测条件所限，目前对小尺度极光弧的观测研究远远不足，亟待确认的问题有：弧宽的空间分布谱是否连续、小尺度极光弧的产生与弥散极光、中大尺度极光弧及其它空间物理参量的相关性等。这些问题的存在制约了对其产生机制的研究。2009年，我国在南极中山站新建了一套小尺度极光成像系统并连续观测至今，本项目拟在充分利用该系统多年观测数据基础上，利用计算机图像处理和模式识别技术，对极光弧进行自动识别，统计弧宽的空间分布特征；研究小尺度极光弧与弥散极光、中大尺度极光弧之间的相关性；结合地面、雷达、卫星等多种观测，分析小尺度极光弧与磁地方时、地磁活动性、电离层特性之间的相关性；结合现有极光弧产生的各种理论，探讨小尺度极光弧的可能产生机制，推动小尺度极光弧研究迈上新台阶。

极光弧是最常见的一种极光形态, 其空间尺度大至数百千米，小至几十米。极光弧宽的研究对理解极光粒子加速机制及磁层-电离层中的跨尺度耦合具有重要意义。本项目基于我国北极黄河站和南极中山站观测数据，重点研究了全天空极光图像的表征、分类、分割，以及多尺度极光弧结构的识别、定位、弧宽测定及弧宽空间分布特征统计等问题。极光形态和动态演变过程极为复杂，至今尚无明确的特征描述和形态分类方法。本项目利用传统局部描述子和深度卷积神经网络表征极光图像形态特征，实现了极光图像有监督和无监督自动分类，从海量极光观测数据中自动识别出极光弧图像。基于自动识别出的极光弧图像，本项目进一步实现了极光弧轮廓自动获取。分别通过人机交互和全自动的方式，实现了在一幅极光图像中定位和分割出感兴趣的极光结构，如极光弧结构。最后，基于检测出的极光弧轮廓，本项目通过定位极光弧法线方向，计算了极光弧的宽度，给出了极光弧宽的空间分布特征统计。此外，本项目还实现了基于行星际/太阳风和地磁条件的紫外极光卵边界建模和预测。该项目研究为进一步研究极光弧发生机制及其与磁层边界层动力学过程的对应关系奠定基础。