## 5 Discussion
### SANAE: Scintillation Events  
During the second period of pronounced negative \(B_{x,\mathrm{IMF}}\) values, which started at around 11:30 UT and ended at around 18:10 UT on 8 September 2017 (red curve in panel a of Figure 1), the GNSS receiver located at SANAE IV base recorded weak/moderate  
Figure 3: GNSS data from the receiver located at Concordia station (DMC0) on 8 September 2017. From top to bottom: Total Electron Content (TEC, **a**), Rate of TEC change (ROT, **b**), phase scintillation index (\(\sigma_{\varphi}\), **c**) and amplitude scintillation index (\(S_{4}\), d). Different colors refer to different satellites in view of the receiver. Red vertical line highlights the local magnetic noon. amplitude scintillations affecting several satellites in view (panels c and d of Figure 2). The southward excursion of the \(B_{\rm z,IMF}\) component led to the equatorward expansion of the auroral oval due to an increased magnetospheric convection, encompassing SANAE IV station within the auroral oval. To confirm this hypothesis, we compared corresponding auroral radiance measurements with amplitude scintillations. Figure 4 shows polar-view maps covering all MLT (00:00-24:00) and \(\left|\,50^{\circ}\,\right|-\left|\,90^{\circ}\,\right|\) AACGM Lat sector of southern hemisphere. Each map displays the auroral radiance at 12:22 UT (a), 13:06 UT (b), 14:04 UT (c), 14:47 UT (d), 15:47 UT (e) and 16:25 UT (f) on September 8. Such times were selected to investigate the ionospheric scenario in which amplitude scintillations were recorded at SANAE IV base. Each map displays the auroral oval boundary location (red dashed contours), as retrieved from the auroral radiance data, and the projection to 350 km of altitude of the amplitude scintillations exceeding 0.1 (magenta diamonds), recorded during the DMSP passage. The projection to 350 km of altitude of all the \(\sigma_{\varphi}\) values with an elevation angle \(\alpha=30^{\circ}\) (purple circles) were reported to identify the field of view of the GNSS receiver along the DMSP track. This enables the comparison between the field of view of the GNSS receiver and the location of the auroral oval. Although the observed scintillation is not collocated with the radiance measurements, the observation of the location of the field of view of the GNSS receiver (purple circles) with reference to the equatorward auroral oval boundary [44; 45] (red dashed contours) shows that amplitude scintillations occurred in the ionospheric cusp. From the literature it is well-known that, in this region, the interaction between polar cap patches and cusp auroral dynamics can trigger strong GNSS phase scintillations [8; 31; 58; 59]. Indeed, between 12:30 and 16:30 UT, the receiver located at SANAE IV base recorded phase scintillations up to \(\sim\)1.0 rad (Figure 2c). This means that irregularities of spatial scale in the range of kilometers (or even more) [3; 60] were in the field of view of the receiver. In addition, the recording by  
Figure 4: Polar-view maps in AACGM latitude and MLT of the austral auroral radiance as measured by SSUSI instrument in the LBHL band at 12:22 UT (**a**), 13:06 UT (**b**), 14:04 UT (**c**), 14:47 UT (**d**), 15:47 UT (**e**) and 16:25 UT (**f**) on 8 September 2017. Each map also reports the auroral oval boundary location (red dashed contours), as retrieved from the auroral radiance data, the amplitude scintillations greater than 0.1 (\(\lx@sectionsign\)4, magenta diamonds), recorded at SANAE IV base during the DMSP passage, and all the \(\sigma_{\varphi}\) values having elevation angle \(\alpha=30^{\circ}\) (purple circles). Scintillation data were projected to 350 km altitude. Each map covers 00:00–24:00 MLT and \(\left|\,50^{\circ}\,\right|-\left|\,90^{\circ}\,\right|\) AACGM Lat, the magnetic noon/midnight is at the top/bottom. GNSS receiver of both phase and amplitude scintillations suggests that significant plasma irregularities were present at all scales.