Research On Small-scale Ionospheric Disturbance Based On High Precision Spaceborne Magnetic Field Data

In this paper,based on the 50 Hz high-frequency magnetic field data measured by Swarm satellites from 2015 to 2019,small-scale ionospheric traveling disturbance(SSTID)detection algorithm was used to detect SSTIDs with a wavelength less than10 km within the magnetic latitude ± 45 °.Furthermore,the DBSCAN(Density-Based Spatial Clustering of Applications with Noise)clustering algorithm was used to eliminate the weak equatorial plasma bubble(EPB)pollution events that were not excluded in the detected SSTID event set.Finally,the statistical characteristics of the SSTIDs were studied.The main work and results of this article are as follows:1.A feasible SSTID detection algorithm is proposed.When using small-scale magnetic field fluctuations as a proxy to detect SSTID,a 1 Hz high-pass filter is used to filter the magnetic field components in the perpendicular and in the parallel direction of the main field,respectively.Then the SSTIDs are detected and the EPB pollution events are eliminate by threshold judgment on the filtered field components,respectively.The results show that the SSTID detection algorithm is basically reliable,but has the defect that it cannot exclude a small number of weak EPB pollution events.2.DBSCAN clustering algorithm was used to exclude EPB contamination in SSTIDs.The dependence of the weak EPB pollution events selected by the clustering algorithm on geographical longitude,month,magnetic local time and solar activity intensity are basically consistent with previous research results.The selected EPB events depend on the intensity of solar activity,and are mainly distributed within magnetic latitude ± ?,geographical longitude-60 to-20 degrees,and in the months between October and March.It appears frequently in the magnetic local time from 20 to 24.3.The small-scale magnetic fluctuations caused by the SSTIDs only appear in the perpendicular direction of the main magnetic field.There is no obvious plasma density disturbance at the height of the Swarm satellite.On the whole,the characteristics of SSTIDs detected by the three Swarm satellites are almost same.The number of events detected by the B satellite(higher orbit)is about 7% less than that of the A / C satellite(lower orbit).4.The occurrence rate of SSTIDs shows obvious geographical,magnetic local time and seasonal dependence characteristics.The SSTID rarely occurs in the magnetic equatorial region(within ± t magnetic latitude).It frequently appears near the magnetic latitude ± t,and the distribution of the event density exhibits obvious magnetically conjugacy in the northern and southern hemispheres.As for longitude,the event distribution has the highest peak in the East Asia/Australia sector,and the other lower peak is in the North Atlantic region.In the South Atlantic Anomaly region(SAA),there is an region of very low event density.The local-time maximum peak of SSTID event density appears at dusk.There is a weaker peak of event density in forenoon,compared to the night events.SSTID has the highest peak and the second peak of the event density on the summer solstice and winter solstice,but hardly happens in equinoxes..The statistical characteristics of the SSTIDs are almost consistent with MSTIDs.Therefore,it can be considered that SSTID is an evolutionary state of MSTID.