Abstract
Ionospheric irregularities can affect satellite communication and navigation by causing scintillations of radio signals. The scintillations are routinely measured using ground-based networks of receivers. This study presents observations of ionospheric irregularities by Langmuir probes on the Swarm satellites. They are compared with amplitude scintillation events recorded by the Global Positioning System-Scintillation Network and Decision Aid (GPS-SCINDA) receiver installed in Mbarara (Lat: 0.6^{circ }hbox {S}, Lon: 30.8^{circ }hbox {E} , Mag. lat: 10.2^{circ }hbox {S}). The study covers the years from 2014 to 2018 when both data sets were available. It was found that the ground-based amplitude scintillations were enhanced when Swarm registered ionospheric irregularities for a large number of passes. The number of matching observations was greater for Swarm A and C which orbited at lower altitudes compared to Swarm B. However, some counterexamples, i.e., cases when in situ electron density fluctuations were not associated with any observed L-band amplitude scintillation and vice versa, were also found. Therefore, mismatches between observed irregularity structures and scintillations can occur just over a few minutes and within distances of a few tens of kilometers. The amplitude scintillation strength, characterized by the S4 index was estimated from the electron density data using the well-known phase screen model for weak scattering. The derived amplitude scintillation was on average lower for Swarm B than for A and C and less in accordance with the observed range. Irregularities at an altitude of about 450 km contribute strongly to scintillations in the L-band, while irregularities at about 510-km altitude contribute significantly less. We infer that in situ density fluctuations observed on passes over or near Mbarara may be used to indicate the risk that ionospheric radio wave scintillations occur at that site.
Highlights
Ionospheric irregularities occur near the geomagnetic equator after sunset and multiple studies have observed the extension of irregularity occurrence after midnight (e.g., Dao et al 2011; Huang et al 2014)
Correspondence between occurrence of ionospheric irregularities and scintillations This section presents the occurrence of ionospheric irregularities observed by Swarm A, B, and C in comparison with simultaneous measurements of S4 index values on the ground
From panel (b) of Fig. 1, it is observed that std(dNe ) clearly captures the fluctuations in Ne between about ±15◦ quasi-dipole latitude (QLat)
Summary
Ionospheric irregularities occur near the geomagnetic equator after sunset and multiple studies have observed the extension of irregularity occurrence after midnight (e.g., Dao et al 2011; Huang et al 2014). Our study continues by comparing the statistical occurrence of ionospheric irregularities and amplitude scintillation and the results are presented .
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