Simultaneous observation on the post-sunset occurrence of travelling ionospheric disturbance alongside ionospheric irregularities over the East Africa low latitude region

Abstract

Using a data set from the network of more than 30 GNSS receivers within the East Africa sector; a study on the transient wave-like total electron content (TEC) modulation alongside the post-sunset irregularities has been presented. The study period is during the years 2019 to 2021 and the year 2014. The TEC modulation was detected from the quasi-periodic variation of detrended TEC and occurs nearly on a day-to-day basis at post-sunset hours just like the post-sunset ionospheric irregularities. The wavelike TEC modulation is likely due to gravity waves generated at the lower atmosphere that propagates into the F region and is quantified as travelling ionospheric disturbance (TIDs). The dominant quasi-periods of these TIDs are between 10 and 50 min. The TIDS, just like the irregularities, were confined in the latitudinal range of 0–9.4oS magnetic latitudes within the East Africa sector. A statistical analysis of simultaneous observations of the post-sunset TIDs shows that the day-to-day variations are identical to that of the ionospheric irregularity occurrence rate. The TIDs exhibit a relatively strong wave oscillation with multiple wavelengths preceding/accompanying the occurrence of irregularities. The simultaneous observation of TIDs and irregularities shows that the wavelike seeding perturbation associated with gravity waves from the lower atmosphere combined with strong seeding forces (unknown source) could facilitate the observed growth rate of the Rayleigh Taylor Instability mechanism that is associated with the formation of ionospheric irregularities. Additional experiments and tropospheric observation may be required to ascertain the source of gravity waves that are linked to TEC perturbation during nighttime hours.