Equatorial and low-latitude ionospheric TEC response to CIR-driven geomagnetic storms at different longitude sectors

Abstract

In this study the response of ionospheric F-region to 18–21 September 2014, 19–24 January 2016, and 07–10 March 2016 CIR-driven storms in the equatorial and low-latitude region of America, Africa, Asia, and Pacific sectors are investigated. TEC data obtained from the Global Navigation Satellite System (GNSS) receivers, located in the four longitude sectors and electron density (Ne) measurements obtained from Swarm-A satellite were used. The storm time behavior of TEC was analyzed by computing its deviation from quiet monthly median TEC (ΔTEC). The rate of change of TEC index (ROTI) and the relative electron density perturbation (ΔNe/Ne) derived from GPS-TEC and Swarm-A, respectively, were used as ionospheric irregularity proxies. In this study, we have also analyzed the ionospheric current disturbances during the storm events using ground-based magnetic data. The result revealed that significant nighttime positive ionospheric storm reaching about 284% (Africa, nklg), 115% (Africa, dakr), and 191% (Pacific, naur) was observed during the storm main phase 19 September 2014, 20 January 2016, and 06 March 2016, respectively. This could be associated with oscillation in the IMF Bz and minimum value in ionospheric current disturbance (Diono). Nighttime negative ionospheric responses were also observed in the American sector during the storm main phase of 18–21 September 2014 and 19–24 January 2016 and in the Asian sector during 18–21 September 2014 events, possibly due to the combined effects of over-shielding/disturbance dynamo electric field and neutral composition change. During the storm recovery phases (21–23 January 2016, 07–10 March 2016), significant positive ionospheric storm were also noticed. The occurrence of ionospheric irregularities was observed over the equatorial and low-latitude region of America and Africa during the main phase of 18–21 September 2014, 19–24 January 2016, and 05–10 March 2016 storm events, possibly related with the enhancement in the zonal electric field observed during dusk period, when oscillation in IMF Bz exists. During main phase of the storms, while the occurrence of ionospheric irregularities over Asian and Pacific longitude sectors are suppressed, it frequently occurs over the American longitude sector. Postsunset behavior of plasma density irregularities observed by Swarm satellites is consistent with the ground-based observation of TEC fluctuations.