Electric field versus neutral wind control of the equatorial anomaly under quiet and disturbed condition: A global perspective from SUNDIAL 86

Developments of equatorial Ionization Anomaly (EIA) under quiescent and disturbed ionospheric conditions are investigated using the data collected from the low-latitude network of ionosondes and magnetometers operated at different longitude sectors of the globe as a part of the SUNDIAL 86 campaign (22 September to 3 October, 1986). Based on case studies of EIA developments, attention is focused on identifiying the EIA response to changes in the electric fields associated with the equatorial electrojet and counter electrojet events. The response time of the EIA to electric field changes is found to vary from 2.5 to 4 h. An anomalous EIA development observed in the morning sector on September 23 suggested possible electric field penetration to low latitude during a substorm energy storage/Dst development phase. The analysis also shows that the afternoon EIA could be inhibited due to equatorward blowing disturbed neutral winds. The results of the present analysis emphasize the need for pursuing further investigations for the response of EIA to magnetosphere-induced disturbances