## 5 Conclusions  
We observed small-scale irregularities as the 22 June 2015 geomagnetic storm evolved. We used spread-F data from ionosonde, and the Cygnus A signal amplitude scintillation data from IISR. The most pronounced effect is observed when the irregularity scale is of the radiowave first Fresnel zone \(\sim\)\(\sqrt{\lambda}\)z (where \(\lambda\) is the signal wavelength, z is the distance to the irregularity). An approximate distance \(z\) is \(\sim\)100(ISSR)/200(ionosonde)\(-\)300 km. As the ionosonde recorded F-spread within the 3-10 MHz band and the Cygnus A signal frequency is 150 MHz, the irregularity size is within \(\sim\)0.5 km (IISR) and \(\sim\)5.5 km (ionosonde) range. The exponential behavior of the irregularity spectrum explains why we did not observe noticeable GPS/GLONASS signal amplitude scintillations. It also explains why the ionosonde signal scintillations were more pronounced than those of Cygnus A (received by IISR). In addition, a longer observation time of small-scale irregularities by the ionosonde may be connected to the radiation pattern difference (ionosonde has a wider radiation pattern than the IISR). The spatial distribution of the TEC variations and the maps for the electric potential from the SuperDARN data revealed that small-scale irregularities are most likely caused by an the auroral oval expansion. Scintillations and the PPP errors at mid-latitudes increased, when the irregularity region with an increased level of the TEC variations approached the measuring facilities. At mid-latitudes, the PPP errors exceeded the background level in the region of small-scale irregularities appearance over several hours by at least fivefold. The following are available online at [[http://www.mdpi.com/2072-4292/12/10/1579/s1](http://www.mdpi.com/2072-4292/12/10/1579/s1)]([http://www.mdpi.com/2072-4292/12/10/1579/s1](http://www.mdpi.com/2072-4292/12/10/1579/s1)), [[http://www.mdpi.com/2072-4292/12/10/1579/s2](http://www.mdpi.com/2072-4292/12/10/1579/s2)]([http://www.mdpi.com/2072-4292/12/10/1579/s2](http://www.mdpi.com/2072-4292/12/10/1579/s2)), [[http://www.mdpi.com/2072-4292/12/10/1579/s3](http://www.mdpi.com/2072-4292/12/10/1579/s3)]([http://www.mdpi.com/2072-4292/12/10/1579/s3](http://www.mdpi.com/2072-4292/12/10/1579/s3)); Video S1: Global dynamics for the GPS PPP error as derived from a ground-based GPS-receiver for 0 through 24 UT on 22 June 2015. The animation cadence is 1 min. The time (in UT) is shown on the top; Video S2: Global dynamics for the 10-20 min TEC variations as derived from a ground-based GNSS-receiver for 17 through 24 UT on 22 June 2015. The animation cadence is 1 min. The scale is on the right. The corresponding UT is shown in the animation title; Video S3: Global dynamics for the 20-60 min TEC variations as derived from a ground-based GNSS-receiver for 17 through 24 UT on 22 June 2015. The animation cadence is 1 min. The scale is on the right. The corresponding UT is shown in the animation title. Conceptualization and Methodology, Y.Y., R.V. and K.R. Data curation and formal analysis: IISR\(-\)R.V., A.S. and M.G. ; Ionosonde\(-\)K.R. and A.V. ; GNSS\(-\)Y.Y., A.Y., A.K. and A.V. PPP calculation and formal analysis, S.S. Investigation, Y.Y., R.V., K.R. and A.V. Writing\(-\)Original Draft Preparation, Y.Y., A.V., R.V. and K.R. Writing\(-\)Review \(\&\) Editing, Y.Y., A.V. and A.Y. All authors have read and agreed to the published version of the manuscript. The research was supported by Russian Federation President Grant No. MK-3265.2019.5 and by Russian Foundation for Basic Research Grant No. 19-05-00889.