利用聚类算法区分小尺度电离层行扰事件与赤道等离子体泡事件

Distinguish Small-scale Traveling Ionospheric Disturbances and Equatorial Plasma Bubbles by Clustering Algorithm

利用Swarm卫星2015年1月1日至2019年12月31日的50Hz高频磁场数据,根据阈值判断垂直于主磁场方向的扰动,对磁纬45°N-45°S之间的小尺度电离层行扰事件进行探测.为避免混淆而产生的干扰,可以根据阈值判断平行于主磁场方向是否发生扰动,从而排除典型的赤道等离子体泡事件.但对于较弱的赤道等离子体泡事件,扰动阈值判断无效.为避免弱赤道等离子体泡事件的污染,根据小尺度电离层行扰事件和赤道等离子体泡事件在不同参数空间中的密度分布差异,利用基于密度的聚类算法将赤道等离子体泡事件进一步甄别提取.结果表明,聚类算法能够有效地将赤道等离子体泡事件从小尺度电离层行扰事件中甄选出来,并使小尺度电离层行扰事件聚类与赤道等离子体泡事件聚类形成清晰的边界.由聚类算法导出的弱赤道等离子体泡事件主要分布在磁纬15°N-15°S,地理经度20°-60°W,月份10至3月之间,并且在20:00MLT-24:00MLT存在高发生率,同时依赖于太阳活动,这也验证了前人的相关研究结果.

By analyzing the 50Hz high-frequency magnetic field data by Swarm from January 2015 to December 2019,according to the magnetic disturbances above the threshold in the perpendicular direction to the main field,Small-Scale Traveling Ionospheric Disturbances(SSTID)within±45°N magnetic latitude have been detected.When detecting SSTID,Equatorial Plasma Bubbles(EPB)can be excluded by determining whether there is magnetic disturbance above the threshold in the direction which is parallel to the mean ambient field.However,when the disturbance is weak,the algorithm cannot completely exclude it.According to the different density distribution of SSTID and EPB in parameter space,the EPB can be distinguished by a density-based clustering algorithm.The results demonstrate that the clustering algorithm is very effective on separating EPB and SSTID in different two-dimensional parameter spaces and brings out a clear boundary between the high density region and low density region.The EPB identified by the clustering algorithm shows the strong dependence on solar activity and their statistical features are consistent with the previous study.