## 3 Results
### Local ROTI Variations  
The TEC behavior observed from the MGEX observations indicates ionosphere scintillation. Thus, some ionosphere irregularities have been generated by this event. To further verify the characteristics of those irregularities, the following studies were focused on ROTI, calculated from the GPS, GLONASS, and BDS observations in the European sector. From 22 June, large ROTI values were observed in the European sector, which was in accordance with previous studies [17; 44], concluding that a super plasma bubble was generated during the storm. With the benefits of the multi-GNSS observations,  
Figure 6: The vertical TEC (VTEC) responses to the storm at the day of year (doy) 174, 23 June ((**a**) VTEC; (**b**) VTEC variation percentage, referred to by Equation (12)). the phenomenon has been further verified. The enhancement of the ROTI during the storm can be contributed to two influential factors: (1) the aurora ovals expansion, with growth of particle precipitation, observed mainly at high latitudes, as Figure 7 demonstrated; (2) the prompt penetration of the electric field, observed mainly at the middle and low latitudes, and contributed largely to ionosphere irregularities at the middle latitudes. In Figure 7, large ROTI values were observed simultaneously, with different time zones in 3 MGEX stations; this was one of the verifications that the storm-induced ionosphere irregularities. The ROTI variations took place mainly in two phases. The first phase started from 18:00 UT on the 22 nd and lasted for around 3 h. The second phase started from 02:00 UT on the 23 rd and gradually vanished after 06:00 UT. The ROTI values of different constellations shared similar temporal characteristics, further supporting the storm-induced ionosphere irregularities from another side. In REYK and KIRU, a pre-storm ROTI variation was observed from 15:00 UT to 17:00 UT, during the local sunset period. The developing patterns of the ionosphere irregularities represented by the ROTI were shown in Figure 8. The red and pink rectangles indicated the location of large ionosphere irregularities, observed by the ROTI. Figure 8a demonstrates the ROTI enhancements in the first sub-phase of the storm and clear irregularity patterns were observed in 35\({}^{\circ}\) W-35\({}^{\circ}\) E, 55\({}^{\circ}\) N-72\({}^{\circ}\) N. The results were consistent with Figure 7. The intensity of the ionosphere irregularities increased in the second sub-phase of the storm, as Figure 8b shows. Another two irregularities appeared in the northern hemisphere, one in the eastern coast of USA and the other across Spain and northern Africa. The responses in the southern hemisphere were also positive. The irregularities were dominant in 90\({}^{\circ}\) W-130\({}^{\circ}\) W, 70\({}^{\circ}\) S-60\({}^{\circ}\) S, with almost a 40-degree longitudinal coverage. Another feature was highlighted in 45\({}^{\circ}\) E-77\({}^{\circ}\) E, 30\({}^{\circ}\) S-50\({}^{\circ}\) S, with increments of irregularities from the first sub-phase of the storm to the second sub-phase of the storm. Noticeable irregularities occurred in New Zealand, with a coverage of 160\({}^{\circ}\) E-180\({}^{\circ}\) E, 30\({}^{\circ}\) S-50\({}^{\circ}\) S. The ionosphere bubbles of this region were further investigated in Section 3.5. Figure 7: The rate of TEC index (ROTI) observed at high latitudes with MGEX data. (blue: GPS; red: GLONASS; green: BDS; pink: GALILEO). Those large-scale simultaneous triggers of the ionosphere irregularities in the middle latitudes, as Figure 8b demonstrates, were considered to be driven by the prompt penetration of electric field (PPEF, [[http://geomag.org/models/PPEFM/RealtimeEF.html](http://geomag.org/models/PPEFM/RealtimeEF.html)]([http://geomag.org/models/PPEFM/RealtimeEF.html](http://geomag.org/models/PPEFM/RealtimeEF.html))) propagating through high latitudes to the middle and low latitudes. Figure 9 shows that the PPEF clearly had two dominant phases coordinated with the storm phases.