## 3 Results
### Spread-F and Scintillations  
Figure 3 shows the experiment geometry. The left panel shows the GPS ionospheric pierce points (IPP) at 300 km as black lines with 10-20 minute TEC variations superimposed, red curves, at 19:30-20:30 on 22 June 2015. The vertical segment in the right bottom part of panel (a) shows 0.5 TECU variations. The data shown are measured by the ISTP SB RAS station within the SibNet. The TEC variations are shown only for four satellites (PRN15, PRN20, PRN21, PRN22). The right panel shows the geometry in details. Black lines show the GPS IPP (the same as on the left panel). Gray lines show the IPP of Cygnus A at 100, 250, and 400 km for the IISR location that is 60 km away from the ISTP SB RAS station. Filled gray region and filled blue region are approximate radiation patterns (at 250 km) of the ionosonde and of the IISR, respectively. The ionosonde was not capable of measuring the direction of the received signals during the interval of interest. Thus, we only can attribute the spread-F data to somewhere in the gray region. Figure 3 allows us to see that the measurements are almost in the same region. We observed the spread-F on 22 June 2015 (Figure 2b) rather than on 23 June 2015. Note that, when the 22 June 2015 H-SYM is minimal at 04:25 UT, there was no noticeable spread-F (Figure 2b). There were occasional black-outs that prevented reliable processing of the ionograms. However, when there is no black-out, there is still no spread-F on the ionograms. The solar wind proton density at this time was even smaller than that of the quiet time. This leads to a smaller energy input into the auroral region; hence, no large-scale disturbances exist and no small-scale irregularities are generated. Figure 2: Evolution of the 22 June 2015 geomagnetic storm from the OMNI data. Panel a: H-SYM index (black line) and the interplanetary magnetic field (IMF) Bz component (blue line). Panel b: AE-index. Panel c: solar wind proton density (black line) and spread-F width (red line). Spread-F data are provided for the Irkutsk ionosonde (52\({}^{\circ}\)N, 104\({}^{\circ}\)E). Figure 4 shows the spread-F width time series from the ionosondes in Irkutsk (_a_) as well as in Yakutsk, Mohe, and Moscow (d). Panel b shows phase scintillations \(\sigma\varphi\) calculated by using observations from all the visible GPS satellites (all the GPS satellite data are mixed here), and Cygnus A radio signal amplitude scintillations (c). The 22 June 2015 data are plotted for 15:00 - 24:00 UT. On the panel c, we also show the 24 June 2015 data (grey) as a quiet time reference. Dashed-dotted line shows the angle \(\gamma\) between the \"IISR - Cygnus A\" line of sight and the Earth magnetic field calculated based on the IGRF\(-\)12 model [51]. We see the spread-F enhancement 19:45 UT through 21:15 UT in Irkutsk. After the magnetic storm onset, the spread-F was at the background level for an extra hour. The background was \(\sim\)0.08 MHz, while the maximal spread-F width was 0.46 MHz at 20:15 UT. We also observed a \(\sigma\varphi\) increase for \(\sim\)19:30-19:50 UT. The \(\sigma\varphi\) mean value was 0.07 rad, with \(\sim\)0.1-0.2 rad during the enhancement. We did not observe any significant increase in the GPS/GLONASS navigation signal amplitude scintillation. During the time interval presented in Figure 4, the S4 index did not exceed the background level, and, hence, we do not show the GPS/GLONASS S4 here. Unfortunately, there are no observations from the Norilsk ionosonde during the storm. Black-out caused by strong absorption in the D-region started shortly after the SSC and prevented collecting useful information from the ionograms. However, we were able to retrieve the data for the ionosondes (see Figure 4d) in Yakutsk (blue line), Mohe (black line), and Moscow (red line). The spread-F is observed at all the stations. A strong spread-F appears at the similar time at Mohe and Moscow. Also, the time was close to that when we observed the spread-F at Irkutsk (20:15 UT, 22 June 2015).