## 5 Discussion
### Concordia: Amplitude and Phase Scintillations
Such spatial scales correspond to the typical PCP dimensions [90; 91; 92] that in L-band scintillations identify large-scale irregularities with respect to the small-scales associated with the first Fresnel radius [3]. The fact that the GNSS receiver recorded amplitude and phase scintillations suggests that even smaller-scale irregularities populated the investigated region, probably caused by the strong variability of plasma dynamics induced by particle precipitation. Indeed, the comparison between scintillation indices (c and d panels in Figure 3) and electron density _rms_ variations (Figure 9) shows that the observed scintillations occurred in correspondence with sharp and sudden variations of the calculated _rms_. Since _rms_ is an estimation of the variation of the electron density, its sharp and sudden increases/decreases between two consecutive orbits suggest a high variability of plasma dynamics. In addition, since the  
Figure 10: Polar-view maps in AACGM latitude and MLT coordinates displaying the different from zero values of the PCP flag estimated by Swarm A (red) and Swarm B (blue) data on 8 September 2017. In each map the projection to 350 km of altitude of all the \(\sigma_{\varphi}\) values recorded by the GNSS receiver located at Concordia, which have elevation angle \(\alpha=30^{\circ}\) (purple circles) are also shown to highlight the receiver’s field of view. Each map reports the observations collected in the time interval displayed on the top of each map. Each map covers 00:00–24:00 MLT and \(150^{\circ}\,|-190^{\circ}\,|\) AACGM Lat, the magnetic noon/midnight is at the top/bottom. electron density _rms_ variations occurred simultaneously to the greatest ROT excursions recorded by the GNSS receiver during the day (Figure 3b), it is possible to say that the observed scintillation may be linked to sudden changes in plasma dynamics. In fact, ROT supplies information about the TEC rate of change being defined as the TEC first time derivative (providing ROT values in units of total electron content unit over one minute, [TECu/min]). Since ROT provides information on plasma dynamics, it allows associating the observed scintillations with variations in plasma dynamics. In this scenario, it is reasonable to argue the presence of ionospheric irregularities. Maps in Figure 11 confirm this hypothesis. Specifically, each map displays TEC data as a function of AACGM latitude and MLT, with a spatial resolution of 1\({}^{\circ}\) AACGM Lat x 4 min MLT. Each map shows TEC data collected every 30 min following the time shown at the top of each map with the projection to 350 km of altitude of all the \(\sigma_{\varphi}\) values having elevation angle \(\alpha=30^{\circ}\) (purple circles) recorded in the same time interval as the TEC data by the GNSS receiver at Concordia. The variability of TEC in adjacent regions, including those regions enclosed in the field of view of the GNSS receiver (highlighted by purple circles), indicates that several irregularities populated the polar cap ionosphere. In addition, inside the receiver's field of view, TEC values appear generally higher than those in the surrounding areas. This scenario suggests the presence of a locally large variability of the plasma dynamics that may have favored the fragmentation of the PCP in irregularities of the order of the first Fresnel radius. Figure 11: Polar-view maps in AACGM latitude and MLT, with spatial resolution of 1\({}^{\circ}\) MLat x 4 min MLT, of the Total Electron Content (TEC) at 14:30 UT (**a**), 15:00 UT (**b**), 15:30 UT (**c**) and 16:00 UT (**d**) on 8 September 2017. Each map shows TEC data collected in the 30 min following the time shown at the top of each map with the projection to 350 km of altitude of all the \(\sigma_{\varphi}\) values having elevation angle \(\alpha=30^{\circ}\) (purple circles) recorded at Concordia in the same time interval as the TEC data. In each map, that covers 00:00–24:00 MLT and 175\({}^{\circ}\) \(|\) – 190\({}^{\circ}\) | AACGM Lat, the magnetic noon/midnight is at the top/bottom.