Ionospheric irregularity behavior during the September 6–10, 2017 magnetic storm over Brazilian equatorial–low latitudes

Abstract

The September 6-10, 2017 two-step magnetic storm was caused by an X9 solar flare followed by a CME. The SSC that occurred at 23:43 UT on day 06 when Sym-H reached about 50 nT, was due to a sudden increase in solar wind. The first step of the storm was caused by a B z southward incursion on day 07. The magnetic index K p reached 08, and the Sym-H magnetic index reached a minimum value of − 146 nT on day 08 at 01:08 UT, ending the main phase. On day 07, the solar wind intensified once again and the auroral index AE reached 2500 nT. During the recovery phase of this first storm, there was another B z southward incursion on day 08 at 13:56 UT when Sym-H reached − 115 nT, and K p reached a value of 08.33, marking the second step of the storm. In this work, the ionospheric irregularity over São Luís (02.5°S, 44.3°W, dip lat − 04.67°) was studied using data from the VHF, Digisonde and GPS receivers. Electron density data from the satellite SWARM-A were also analyzed for those orbits close to São Luís, and they presented large fluctuations during the storm night of 07/08. To analyze the latitudinal effects of the storm on the plasma irregularities, GPS data from 6 Novatel receivers were used. The vertical plasma drifts during daytime hours were determined using magnetometer data and during the evening using ionogram data. Compared to the 'quiet' days of September 2017, the VHF and GPS S4 amplitude scintillation indices increased substantially during the night of 07/08 when there was a strong intensification in the vertical plasma drift due to a prompt penetration under shielding magnetospheric electric field of eastward polarity. On the other hand, on the night of 08/09 the ionospheric scintillation was completely inhibited due to the disturbance dynamo electric field of westward polarity associated with the first and second storms. The irregularity zonal drifts measured by a VHF receiver around 24 UT (21 LT) were eastward on the nights of 05/06 and 06/07; however, during the night of 07/08, it reversed to westward.

Performance of 6 Different Global Navigation Satellite System Receivers at Low Latitude Under Moderate and Strong Scintillation

“…The S 4 and σ ϕ indexes data from these receivers are analyzed for the geomagnetically quiet (Kp < 3) nights February 20–21, 2013 for the PRN 19 and November 27–28, 2013 for the PRN 25. For geomagnetically disturbed nights the scintillation normally presents high variability (de Paula et al., 2019), so for this study it was selected these two magnetically quiet nights. The daily averaged F10.7 cm solar fluxes for the days February 27, February 28, November 27, and November 28 on 2013 were 111.0, 106.2, 125.6, and 129.3 sfu, respectively, where 1 sfu = 10 −22 Wm −2 Hz −1 .…”

“…Those plasma density irregularities with scale sizes of hundreds of meters cause scattering and diffraction of radio waves propagating through these unstable ionospheric regions and can produce large amplitude and/or phase scintillation on the received signals (Yeh and Liu, 1982). The scintillation strength is strongly dependent of the local time, season, solar flux, propagation path, magnetic location and geomagnetic conditions (Muella et al, 2017;Sousasantos et al, 2018;Moraes et al, 2018a;2018b;de Paula et al, 2019).The fades on the GNSS signals due to scintillations caused by irregularities with scale sizes between 300-400 m can be deep and long enough to cause GNSS receivers to lose lock, thus affecting the positional and navigational accuracy. Also, as pointed out by several authors (Skone et al, 2001;Doherty et al, 2004;Zou and Wang, 2009), rapid phase variations can modify the Doppler shift in the GPS signal, causing it to exceed the bandwidth of the phase lock loop, resulting in a loss of phase lock.…”

“…Those plasma density irregularities with scale sizes of hundreds of meters cause scattering and diffraction of radio waves propagating through these unstable ionospheric regions and can produce large amplitude and/or phase scintillation on the received signals (Yeh & Liu, 1982). The scintillation strength is strongly dependent of the local time, season, solar flux, propagation path, magnetic location and geomagnetic conditions (de Paula et al., 2019; Moraes, Vani, Costa, Abdu et al., 2018; Moraes, Vani, Costa, Sousantos et al., 2018; Muella et al., 2017; Sousasantos et al., 2018). The fades on the GNSS signals due to scintillations caused by irregularities with scale sizes between 300 and 400 m can be deep and long enough to cause GNSS receivers to lose lock, thus affecting the positional and navigational accuracy.…”

“…Many different scintillation monitors with multi‐frequency and multi‐constellation possibilities have been developed in the last decade. Devices from different manufacturers have been used in different studies and sometimes data analysis involves using data from different equipments (Alfonsi et al., 2018; de Paula et al., 2019; Fortes et al., 2015). A question that arises is how closely the result of these equipments can agree.…”

Climatology of Ionospheric Amplitude Scintillation on GNSS Signals at South American Sector During Solar Cycle 24

“…Several works have investigated the ionospheric scintillation at the SA sector at some periods of solar cycle 24, which has just ended (e.g., De Rezende et al, 2010;Sreeja et al, 2011;Bougard et al, 2013;Alfonsi et al, 2013;Spogli et al, 2013aSpogli et al, , 2013bCesaroni et al, 2015, Khadka et al, 2016Muella et al, 2017;Correia et al, 2018;Guo et al, 2019;De Paula et al, 2019;Oliveira et al, 2020). Some of these works are worthwhile to highlight.…”