Solar flare and radio burst effects on GNSS signals and the ionosphere during September 2017

Strong solar flare events can occur even during the decay phase of the solar cycle. During these events concurrent increases in the X-ray and Enhanced UV (EUV) fluxes and solar radio bursts (SRBs) can be observed. The SRBs cover a large range of frequencies including the L band, giving rise to signal fades in the GNSS carrier-to-noise ratio and fluctuations in its amplitude and phase. The increases in the X-ray, UV, and EUV fluxes cause increase in the ionospheric D, E, and F region electron densities. The aim of this work is to analyze the effects in the GNSS signal, in the ionosphere and in the magnetic field H component of the X9.3 and X1.3 solar flares that occurred on 06 and 07 September 2017, respectively. Data from a network of six GNSS receivers, two magnetometers, and four Digisondes are used in the analysis. Fades of about 5 and 10 dB were observed in the signals of GNSS L1 and L2/L5 frequencies, respectively. Significant positioning errors, were observed for the strongest X9.3 flare. A sudden increase in Total Electron Content with the rates of 2.5–5.0 TECU/min was observed. An increase in the E layer density gave origin to an increase in the Equatorial Electrojet intensity, whose signatures were observed in the H component of two magnetometers. Another observed effect was the ionospheric D region density increase that caused disruption in the Digisonde signal. As a consequence of the described effects, GNSS receivers may fail to produce accurate navigation solution.