Perturbation electric fields and disturbance currents investigated during the 25 September 1998 great storm

Abstract

This study investigates the ionosphere's response to the 25 September 1998 great storm and utilizes multi‐instrument observations covering the Australian (140°E; geographic) and Indian (75°E) longitude sectors. Results show the domination of eastward (westward) electrojet at 140°E (75°E). Its causative net eastward (westward) perturbation electric (E) field drove the forward (reverse) plasma fountain, caused the presence (absence) of the equatorial ionization anomaly (EIA). These strong longitudinal differences were due to a combination of various LT‐dependent, E field‐driven, and competing mechanisms. Perturbation E fields are identified as prompt penetration E field (PPEF) and disturbance dynamo E field (DDEF). Due to the later (earlier) local time at 140°E (75°E), the undershielding PPEF was eastward (westward) directed early in the main phase. A series of periodic substorms occurred during the recovery phase. The substorm‐related eastward PPEFs became overpowered by westward DDEFs over India but remained dominant in the Australian sector. Thus, eastward PPEFs (westward DDEFs) dominated at 140°E (75°E). At 140°E these eastward PPEFs exhibited a strong positive correlation with the variations of both the cross polar cap potential drop and the asymmetric ring current, significantly increased the net equatorial upward E × B drift and thus caused EIA development with plasma bubbles scintillating GPS signals. Based on the strong and independent correlation of these asymmetric ring current events with both the EIA development and the scintillation activity, we propose that the ASY‐H index could provide a natural tool for modeling EIA development and scintillation episodes during severe storms characterized by periodic substorm‐related eastward PPEFs.

Positive and negative GPS‐TEC ionospheric storm effects during the extreme space weather event of March 2015 over the Brazilian sector

“…On the other hand, the present investigation very clearly shows the EIA east-west differences using two chains of 10 GPS stations, each (from equator to beyond EIA crest). In Addition, different longitudinal ionospheric responses were investigated in different sectors such as American, Indian, African, and Asian [de Abreu et al, 2014;Dmitriev et al, 2013;Horvath and Lovell, 2014;Sharma et al, 2011;Sahai et al, 2009aSahai et al, , 2009b.…”

Spatial Gradients in Geomagnetic Storm Time Currents Observed by Swarm Multispacecraft Mission

“…Geomagnetic storms have been explored extensively from the ground as well as spaceborne platforms (Abdu et al, 2006;Dunlop et al, 1988;Horvath & Lovell, 2014;Liemohn et al, 2001;Munsami, 2000;Rangarajan, 1989;Sugiura, 1964;Weygand & McPherron, 2006). It has been realized that the presence of field-aligned currents (FACs), ionospheric closure currents, substorm current wedge, magnetopause currents, magnetotail currents, prompt penetration electric fields, etc., during storm time can cause asymmetry in the ring current (Akasofu & Chapman, 1964;Dubyagin et al, 2014;Friedrich et al, 1999;Greenspan & Hamilton, 2000;Liemohn et al, 2001;Siscoe & Crooker, 1974;Turner et al, 2000).…”