## 4 Scintillation Events  
Figures 2 and 3 show TEC (a), ROT (b), \(\sigma_{\varphi}\) (c) and \(S_{4}\) (d) time profiles recorded on 8 September 2017, by the GNSS receivers SNA0 and DMC0 located at SANAE IV and Concordia stations, respectively. Different colors refer to different satellites entering the receivers' fields of view. For both GNSS stations, TEC data (panels a in Figures 2 and 3) show profiles that deviated from the quiet time diurnal variation, which typically maximize in the local noon/post noon sector (around 12:00 UT for the SNA0 receiver and around 08:00 UT for the DMC0 receiver). The increase of TEC was characterized by values much higher than expected for quiet times, which usually do not exceed 20 TECu (Total Electron Content unit, 1 TECu = \(10^{16}\) el m\({}^{-2}\), e.g., References [46; 57]).  
Figure 1: Interplanetary space observations and geomagnetic response at high latitudes on 8 September 2017. From top to bottom: (**a**) Interplanetary Magnetic Field (IMF) intensity (black), IMF \(B_{y,\text{IMF}}\) component (blue) and IMF \(B_{x,\text{IMF}}\) component (red); (**b**) solar wind (SW) velocity \(V_{\text{SW}}\) (black) and SW dynamic pressure \(P\) (red); and (**c**) \(AE\) (black), \(AU\) (green) and the \(AL\) (red) indices. IMF and SW data are taken from the OMNI database.  
Figure 2: GNSS data from the receiver located at SANAE IV base (SNA0) 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 refers to different satellites in view of the receiver. Red vertical line highlights the local magnetic noon.  
The SNA0 receiver recorded TEC increases (Figure 2a) during the nighttime (00:00-04:00 UT), in the early afternoon (12:00-17:00 UT), around 18:00 UT and between 20:00 and 21:00 UT. Such increases were characterized by rapid TEC fluctuations, as demonstrated by ROT data (Figure 2b), and associated with moderate/strong phase fluctuations (Figure 2c) with low or no amplitude scintillations, except between 12:00 and 16:00 UT when SNA0 recorded moderate amplitude scintillations (S4 \(\sim\)0.4, Figure 2d) affecting several satellites in view. We recall that, according to [PERSON] et al. [8], a scintillation event is considered of moderate to intense level when \(S_{4}\) and \(\sigma_{\varphi}\) are both greater than 0.25, while scintillation is considered to be weak when \(S_{4}\) and \(\sigma_{\varphi}\) are both between 0.1 and 0.25. In addition, only when both \(S_{4}\) and \(\sigma_{\varphi}\) simultaneously exceed 0.25 the scintillation is actually occurring (see, e.g., References [27; 29]).  
The DMC0 receiver recorded TEC increases between 00:00 and 04:00 UT and between 12:00 and 20:00 UT (Figure 3a), which were characterized by intense ROT fluctuations (Figure 3b). Simultaneously, the receiver recorded moderate/intense phase fluctuations (Figure 3c), often associated with weak/moderate amplitude scintillations (Figure 3d). The values of \(S_{4}\) index recorded by the DMC0 receiver during the day (Figure 3d) are higher than those recorded by the SNA0 receiver, even though the data treatment was the same for both stations.