The refractive and diffractive contributions to GPS signal scintillation at high latitudes during the geomagnetic storm on 7–8 September 2017

Abstract

Different indices have been used to reflect, or monitor the ionospheric scintillation, e.g. the detrended carrier phase, δφ, S4, the rate of change of the total electron content index (ROTI), as well as the ionosphere‐free linear combination (IFLC) of two carrier phases. However, few studies have been performed to investigate the refractive and diffractive contributions to these indices, especially during geomagnetic storms. In this study, we analyze the high-resolution (50 Hz) phase and amplitude measurements from four high-latitude stations in Svalbard, Norway during the geomagnetic storm on 7-8 September 2017. Our results show that at high latitudes, the high-pass filter with a standard cutoff frequency of 0.1 Hz sometimes cannot effectively remove the refraction driven phase variations, especially during the geomagnetic storm, leading to a remaining refraction contribution to the detrended carrier phase and δφ when scintillation happens. In the meanwhile, as ROTI is sensitive to the TEC gradients, regardless of small- or large-scale ionospheric structures, both refraction and diffraction effects can cause visible fluctuations of ROTI. For most of the scintillation events, the phase indices (including detrended carrier phase, δφ, and ROTI), IFLC and S4 show consistent fluctuations, indicating that diffraction usually occurs simultaneously with refraction during scintillation. One interesting feature is that although the IFLC and S4 are thought to be both related to the diffraction effect, they do not always show simultaneous correspondence during scintillations. The IFLC is enhanced during the geomagnetic storm, while such a feature is not seen in S4. We suggest that the enhanced IFLC during geomagnetic storm is caused by the increased high-frequency phase power, which should be related to the enhanced density of small-scale irregularities during storm periods.

Investigation of Ionospheric Small‐Scale Plasma Structures Associated With Particle Precipitation

“…with f being the signal carrier frequency and the electron density n e is integrated along the raypath dL (Kashcheyev et al, 2012;Zheng et al, 2022). For propagation paths, which are assumed to be the same for different carrier frequencies, the R corr ratio of two carrier waves is given by…”

“…with the two carrier frequencies f 1 and f 2 and the corresponding carrier phases ϕ L1 and ϕ L2 . The ionospheric refractive index correction term R corr is now removed and the IFLC is non-refractive (Carrano et al, 2013;Cordes et al, 1986;McCaffrey & Jayachandran, 2019;Zheng et al, 2022). The IFLC is then considered at the same rate of the I c and Q c samples, that is, 50 Hz.…”

“…The ionosphere‐free linear combination is then calculated by: $$$IFLC=\frac{{f}_{1}^{2}{\phi }_{L1}-{f}_{2}^{2}{\phi }_{L2}}{{f}_{1}^{2}-{f}_{2}^{2}}=r+\frac{{f}_{1}^{2}}{{f}_{1}^{2}-{f}_{2}^{2}}\lambda N-\frac{{f}_{2}^{2}}{{f}_{1}^{2}-{f}_{2}^{2}}\lambda N,$$$ with the two carrier frequencies f 1 and f 2 and the corresponding carrier phases ϕ L 1 and ϕ L 2 . The ionospheric refractive index correction term R corr is now removed and the IFLC is non‐refractive (Carrano et al., 2013; Cordes et al., 1986; McCaffrey & Jayachandran, 2019; Zheng et al., 2022). The IFLC is then considered at the same rate of the I c and Q c samples, that is, 50 Hz.…”

Nightside High‐Latitude Phase and Amplitude Scintillation During a Substorm Using 1‐Second Scintillation Indices

“…The refractive effects become particularly large in the high‐latitude ionosphere, where plasma flow speeds are large, and the detrending cutoff frequency should be raised to remove the refractive effects (Forte & Radicella, 2002; Spogli et al., 2021). Recent studies have shown that the Fresnel frequency at high latitudes is close to 1 Hz as opposed to ∼0.1 Hz (Ghobadi et al., 2020; Madhanakumar et al., 2022; Zheng et al., 2022). The relation between scintillation and aurora should be revisited using a higher cutoff frequency to remove the refractive effects.…”

Effects of the Relative Dynamics of Ionospheric Irregularities and GPS Satellites on Receiver Tracking Loop Performance

“…Trans‐ionospheric satellite signals intersecting such ionization irregularities inside an electron density depleted region, often termed as “bubble” (Basu et al., 1999; DasGupta et al., 2006; Jiao & Morton, 2015; Pi et al., 1997) lead to diffraction of the signal, which results in random and rapid fluctuation in received signal amplitude and phase, commonly known as scintillation (Aarons, 1982; Aarons & Basu, 1994; Jiao & Morton, 2015), measured in terms of amplitude ( S 4 ) and phase scintillation index ( σ Ø ). Refractive effects on a transionospheric radio signal, caused by the ionosphere, is deterministic in nature, as it is related to the frequency of the signal and the electron density along the signal path (Ghobadi et al., 2020; Zheng et al., 2022). However, diffractive effects are caused by small‐scale ionospheric irregularities that lead to stochastic variation of the signal received at ground (Conroy et al., 2022; Spogli et al., 2021).…”