Large Scale Traveling Ionospheric Disturbances During Geomagnetic Storms of 17 March and 23 June 2015 in the Australian Region

Large scale traveling ionospheric disturbances (LSTIDs) can be detected using the critical frequency of F-2 layer (f(o)F(2)) of the ionosphere. The HF interferometry (HF-int) technique is applied to the ionosonde data from low and mid latitude stations over Australia. For the first time, we present a comparison of TIDs detected during the geomagnetic storms of 17 March and 23 June 2015. The TID response for these two comparable superstorms is significantly different owing to the differing storm evolution patterns. The storm associated TIDs are more intense and longer compared to the solar terminator. Results demonstrate that the morphology of parameters continually varies over time due to highly dynamic ionospheric response to geomagnetic storms. For the March storms, TIDs velocities were 400-700 m/s at the onset phase, similar to 500 m/s during the main phase and similar to 600 m/s during the recovery phase. Their propagation directions were equatorward with east/west deviations. Lower period (similar to 60 min) TIDs were determined during storm onset whereas higher periods (similar to 140 min) were detected during the recovery phase. The June storm produced a different response. The TID velocity at the onset phase was similar to 500 m/s but during the main and recovery phases the velocities were greater than 1,000 m/s. There were large deviations in velocity vectors at the different stations suggesting multiple sources of TID generation and possible resonating effects at middle and low latitude stations. Our findings indicate that while TID detection and storm phases co-occur, the propagation characteristics of TIDs change dramatically throughout the storm.