## 5 Discussion
### Concordia: Amplitude and Phase Scintillations  
The variations of scintillation parameters recorded on 8 September 2017, by the receiver located at Concordia (Figure 3) mainly occurred concurrent with negative excursions of the \(B_{\rm z,IMF}\) (red curve in panel a of Figure 1). This condition led to a large amount of particles precipitating in the high-latitude ionosphere, as confirmed by Figure 9.  
This figure displays the variations of the electron density root mean square (_rms_) by Swarm A (SWA, dots) and Swarm B (SWB, stars). Specifically, _rms_ is calculated for each electron density time series related to a polar crossing of each Swarm satellite over an area spanning 70\({}^{\circ}\) AACGM latitude. By comparing electron density _rms_ (Figure 9) and \(B_{\rm z,IMF}\) (Figure 1, red curve in panel a) variations, we see that, between 00:00 and 02:30 UT and between 12:00 and 17:30 UT, i.e., when \(B_{\rm z,IMF}\) was southward, huge increases in the _rms_ values observed by both satellites occurred. Conversely, when \(B_{\rm z,IMF}\) was northward or near null, the _rms_ intensity decreased. Hence, since _rms_ variations essentially trace the \(B_{\rm z,IMF}\) profile, it is possible to relate the electron density increases highlighted by increases in _rms_ with the particle precipitation caused by southward \(B_{\rm z,IMF}\). Since electron density increases suggests the presence of patches [86; 87; 88], we investigated the behavior of PCP flag over the Southern Hemisphere during the analyzed geomagnetic storm. In fact, contrary to the case of the GNSS receiver located at SANAE IV base, whose field of view looks at latitudes not covered by the PCP flag, at the magnetic latitudes covered by the receiver's field of view at Concordia we can take advantage of the information provided by this index. Figure 10 shows the PCP flag estimated by Swarm A (red) and Swarm B (blue) measurements. Specifically, each map displays PCP flag values different from zero (i.e., presence of polar cap patches), collected by both Swarm satellites in the time interval shown on the top of each panel, and the projection to 350 km of altitude of all the concurring \(\sigma_{\varphi\varphi}\) values having elevation angle \(\alpha=30^{\circ}\) (purple circles) recorded by the GNSS receiver at Concordia. This enables a comparative investigation between the occurrences of patches and GNSS scintillation. The comparison between maps in Figure 10 and the \(B_{\rm z,IMF}\) trend (red curve in panel a of Figure 1) shows that during southward \(B_{\rm z,IMF}\) the values of the PCP flag confirm the presence of patches. In addition, Figure 10 shows that Swarm satellites detected patches both close to and inside the GNSS field of  
Figure 9: Electron density root mean square (_rms_) by Swarm A (dots) and Swarm B (stars) on 8 September 2017, in the Southern Hemisphere. The AACGM latitude ranges between 70\({}^{\circ}\) and 90\({}^{\circ}\) S.  
view during scintillation events (see panels c and d of Figure 3), thus suggesting that PCP could have caused the corruption of the corresponding GNSS signals [11; 13]. The variations of scintillation parameters as shown in Figure 3 further support this hypothesis. Indeed, scintillations (panels c and d) recorded at Concordia between 00:00 and 04:00 UT and between 12:00 and 20:00 UT on September 8 occurred together with high TEC values (panel a) and intense ROT variations (panel b). According to [PERSON] et al. [42] and [PERSON] et al. [8], this suggests that the investigated regions were populated by irregularities of largely varying spatial scales. In fact, the relation between ROT and Nyquist period [43] allows retrieving the irregularities scale length involved in scintillations [8]. So, since at high latitudes experimental evidence shows that plasma convection velocities span a range between 100 m/s and 1 km/s [89], the relative irregularities scale length, sampled by ROT, varies from a few kilometers to tens of kilometers [60].