On the Relationship between Low Latitude Scintillation Onset and Sunset Terminator over Africa

Abstract

The solar terminator is a moving boundary between day-side and night-side regions on the Earth, which is a substantial source of perturbations in the ionosphere. In the vicinity of the solar terminator, essential parameters like S4 index measurements are widely analyzed in order to monitor and predict perturbations in the ionosphere. The utilization of the scintillation index S4 is a well-accepted approach to describe the amplitude/intensity fluctuation of a received signal, predominantly caused by small-scale irregularities of the ionospheric plasma. We report on the longitudinal daily and seasonal occurrence of GNSS signal scintillations, using the data derived from the GNSS stations in Bahir Dar, Ethiopia, Lomé, Togo and Dakar, Senegal. The observed seasonal climatology of GNSS signal scintillations in equatorial Africa is adequately explained by the alignment of the solar terminator and local geomagnetic declination line. It should be pointed out that the strongest scintillations are most frequently observed during the time when the solar terminator is best aligned with the geomagnetic declination line. At all three stations, the comparison of computational and observational results indicated that the scintillation activity culminated around equinoxes in the years 2014, 2015 and 2016. Comparatively, the western equatorial Africa sector has the most intense, longest-lasting, and highest scintillation occurrence rate in equinoctial seasons in all three years. For the first time, we show that the seasonal variation of the scintillation peaks changes systematically from west to east at equatorial GNSS stations over Africa. A detailed analysis of the solar day–night terminator azimuth at ionospheric heights including the time equation shows that the scintillation intensity has a maximum if the azimuth of the terminator coincides with the declination line of the geomagnetic field. Due to the remarkable change of the declination by about 10° at the considered GNSS stations, the distance between scintillation peaks increases by 46 days when moving westward from the Bahir Dar to the Dakar GNSS station. The observations agree quite well with the computational results, thus confirming Tsunoda’s theory.

Ground-based infrastructure for improved space weather specification at low latitudes

“…Required is a systematic deployment of such high-rate GNSS receivers in a coordinated fashion, e.g., together with ionosondes, to utilize the complementary view on ionospheric processes and to derive the equivalent slab thickness of the ionosphere that provides additional information on the shape of electron density profiles [e.g., . A systematic deployment of high-rate GNSS receivers as it has been realized in the MONITOR project in Africa [Beniguel, 2019] in recent years is able to contribute to studies of latitudinal/longitudinal and seasonal occurrence of radio scintillations in relation to underlying ionospheric physics [e.g., Mersha et al, 2021], plasma bubble detection [e.g., Mersha et al, 2020] and drifts [e.g., Kriegel et al, 2017]. Deployments should be done with at least three receivers, separated by ~1 km, deployed at a given site to enable EPB drift measurements.…”

Systematic study of ionospheric scintillation over the indian low-latitudes during low solar activity conditions

“…The formulae used to calculate values of ROT and ROTI are The dominant mechanism, in the onset of amplitude scintillations, is the Pre-reversal Enhancement generated as a result of the enhancement in the vertical E×B drift due to the eastward electric field at the sunset terminator (where the terminator implies a moving boundary between the day side and night side regions on the Earth) generating EPBs and ESFs around this time (Fejer et al, 1999;Woodman, 1970;Ghosh et al, 2020). (Mersha et al, 2021) in their study have brought forward the relationship between the onset of low-latitude scintillation and the sunset terminator. It is also to be noted that the onset of scintillation at a given location represents the time when the irregularities, that produce these scintillations, are initially generated (Liu et al, 2015b).…”

Ionosphere Heterogeneities at Dawn−Dusk Terminator Related to the Starlink Satellites Launch Disaster on 3−8 February 2022

“…As noted by Galushko et al (1998), among all gravity waves sources, the solar terminator holds a special significance, since it is a well-defined and predictable phenomenon. The solar terminator effects in the atmosphere and ionosphere have been explored earlier by different authors (Afraimovich, 2008;Afraimovich et al, 2009;Brady & Crombie, 1964;Colonna & Tramutoli, 2021;Forbes et al, 2008;Gulyaev & Gulyaeva, 1984;Mersha et al, 2021;Miyoshi et al, 2009;Somsikov, 1995). Gravity waves with periods from a few hours down to 5 min must have impact on the charged particles variability at solar terminator similar to the neutral atmosphere density and temperature, Total Electron Content (TEC) scintillation S4 index, sporadic E layer, etc.…”

“…Gravity waves with periods from a few hours down to 5 min must have impact on the charged particles variability at solar terminator similar to the neutral atmosphere density and temperature, Total Electron Content (TEC) scintillation S4 index, sporadic E layer, etc. (Forbes et al, 2008;Haldoupis et al, 2004;Mersha et al, 2021;Miyoshi et al, 2009;Oikonomou et al, 2023). We investigate the differences of TEC variation at the sunrise and sunset solar terminator (ST h ) at an altitude h = 300 km above the Earth during the Starlink launches.…”