Ionospheric disturbances in the African low-latitude region during the space weather event of September 2017

Abstract

The space weather event from September 5-11, 2017, was marked by high activity, with multiple solar flares and a geomagnetic storm. This study investigates the impact of solar flares and the associated geomagnetic storm on the equatorial and low-latitude region of Africa, utilizing data from the Global Navigation Satellite System (GNSS), in-situ electron density observations from the SWARM-A satellite, and ground-based magnetometer data from Mbour (mbo, 14.39^∘S, 16.96^∘W), Dakar, as well as the real-time prompt penetration equatorial electric field model (PPEFM). The analysis of ionospheric total electron content (TEC) disturbances involves comparing storm-time TEC with the mean of the quiet days of the month. The rate of change of TEC index (ROTI) and the rate of plasma density irregularity index (RODI) are employed to examine ionospheric irregularities on the equatorial and low-latitude African longitude. In order to analyze the TEC changes in the ionosphere due to solar flares, difference between the TEC value before the flare and the peak TEC value during the flare were used. Results of the study show that while the X2.2 solar flare did not significantly increase TEC, the X9.3 flare caused a notable enhancement, with TEC increase of 2.47 and 1.66 TECU in the East and West African sectors, respectively. While the X1.3 solar flare caused TEC increase of 1.03 and 0.44 TECU in the East and West African sectors, respectively. Sometimes, reduction in ionospheric TEC were also observed. The ionospheric TEC response during the first stage of the storm’s main phase was minimal, but significant variations were noted during the second stage of the storm’s main phase, in both Eastern and Western African sectors. Ionospheric irregularities during the first stage of the storm’s main phase were suppressed/enhanced in the Eastern/Western African sectors. On the other hand, during the second stage of the storm’s main phase, the occurrence of ionospheric irregularities were inhibited in both African sectors. This may be likely due to the decrease in the pre-reversal enhancement of the ionospheric zonal electric field. Lastly, the study also examines disturbances in ionospheric currents inferred from ground-based data, extracted from magnetometer located in the West African sector. Unfortunately, there is no magnetometer located in the East African sector.