Structures of Multiple Large-Scale Traveling Ionospheric Disturbances Observed by Dense Global Navigation Satellite System Networks in China

The propagation features of three groups of multiple large-scale traveling ionospheric disturbances (LSTIDs), which formed on 22 June 2015 during the passage of LSTIDs that propagated in different directions simultaneously over China, were investigated using the total electron content data from 341 Global Navigation Satellite System stations. The ranges of the periods and horizontal phase velocities of the LSTIDs were similar to 40-120 min and similar to 209-750 m/s, respectively. The first two groups were observed during 0700-1400 UT. The meeting of LSTIDs propagating in opposite directions yielded a differential of total electron content (DTEC) variation net structure, where the enhancement and reduction of DTEC amplitude appeared successively and reached a maximum amplitude of similar to 16% in the overlapping areas. DTEC series based on the observations of geostationary satellites from China's BeiDou Navigation Satellite System addressed the propagation and meeting of fronts. The third group contained two southward propagating LSTIDs, a northward LSTID, and a northwestward one. The joint propagation of the northward LSTID and northwestward LSTID led to a large-amplitude mixed front, which was broadened both in latitudinal and meridional range. The mixed front moved northward at a distance of similar to 1,500-km until it separated into two fronts, due to the difference in propagation velocities and directions. After separation, the northward LSTID continued to propagate and encountered a southward LSTID. The northwestward LSTID dissipated within 30 min in the northwest of China. Such multi-LSTIDs have mainly been observed previously in equatorial regions, and our observations imply that the propagation of LSTIDs in the mid and low latitudes is more complicated than previously reported.