## 4 Discussion
Figure 6: Maps for the electric potential from the SuperDARN data for 18:30 UT (**a**), 18:40 UT (**b**), 19:00 UT (**c**), 19:30 UT (**d**), 20:00 UT (**e**), 20:30 UT (**f**), 21:00 UT (**g**), 21:30 UT (h). Green dashed curve shows the Heppner–Maynard boundary. Figure 7: Maps of 10–20 min TEC variations for 18:30 UT (**a**), 19:00 UT (**b**), 19:30 UT (**c**), 20:00 UT (**d**), 20:30 UT (**e**), 21:00 UT (**f**). Scale is shown at the bottom in TECU units. We recorded a TID in the Northern Hemisphere with an extended wave front. In Figure 7f, we see large positive TEC variations crossing the equator in the American region. According to the movie (see Supplementary Materials, Videos S2 and S3), the disturbance originated in the Northern Hemisphere,  
Figure 8: Maps of 20–60 min TEC variations for 18:30 UT (**a**), 19:00 UT (**b**), 19:30 UT (**c**), 20:00 UT (**d**), 20:30 UT (**e**), 21:00 UT (**f**). Scale is shown at the bottom in TECU units. crossed the equator, and reached \(\sim\)40\({}^{\circ}\)S. The disturbance, hence, travels more than 10,000 km from its source. The disturbance can be seen in the American and Australian longitude sectors, which implies that it is \(\sim\)200\({}^{\circ}\) wide in longitude. It can be clearly identified in the American-Atlantic region, especially, when it was reaching the equatorial region (see Figure 7e, Figure 7f). TID is also seen over the European region, and a part of its structure can be found over Northern Africa. It is difficult to clearly identify TID southward over the Northern African and Asian regions due to low data coverage. Finally, we can compare the TEC variations maps with the maps for the PPP quality. The observed PPP error does not coincide with the sharp oval extension (Figure 6). The oval reached 50\({}^{\circ}\) magnetic latitude in the Asian sector quickly, while the PPP deterioration at such latitudes was recorded only at \(\sim\)20 UT. However, TEC variation maps (Figure 7, Figure 8 and Movies S1, S2) also show a gradual propagation of irregularities from the oval. Moreover, in the American sector, we do not observe any \"propagation\" of the PPP error to the Southern Hemisphere, as we observe for TIDs. If the TID was the source for scintillations resulting in enhancement in PPP errors at mid-latitudes, we would expect to see an increase in PPP error along the TID propagation trajectory. However, we did not observe any \"propagating\" pattern (up to the Southern Hemisphere) in PPP error distributions. While this is not an incontrovertible conformation, it indirectly indicates that TID propagation is not a source for the increase in PPP error (and scintillations). In contrast, this is additional evidence in favor of the auroral oval expansion mechanism for the revealed small-scale irregularities. Thereby, the auroral oval expansion and the development of small-scale structure seem to be a more preferable mechanism to produce the observed small-scale irregularities at mid-latitudes. The irregularities lead to increased phase scintillations of navigation signal. The increase is more pronounced at the start of the irregularity formation. Phase scintillations decay very quickly. We observed spread-F, Cygnus A signal amplitude scintillations, and GPS phase scintillations simultaneously. The spread-F width maximum was recorded after the GPS phase scintillations recover their background level. The \(\sim\)2.5-5.5 km irregularities (ionosonde) seem to persist over the entire interval, when the spread-F is observed. The \(\sim\)400-800 m irregularities (IISR) emerged after the GPS phase scintillations started and ended before the enhanced spread-F ended. We refer the absence of the GPS signal amplitude scintillations to the exponential shape of the irregularity spectrum. Consequently, the irregularities with the size proper for a significant effect on the navigation signal had too low amplitudes to affect the latter. The results on the PPP error agree, in general, with those obtained by [PERSON] et al. [30]. However, while [PERSON] et al.