Effects of interplanetary electric field on the development of an equatorial spread F event

[1] On a geomagnetically disturbed night (7 January 2005), an equatorial spread F (ESF) event was captured during premidnight hours by the Indian MST radar (operated in ionospheric mode) at Gadanki (13.5°N, 79.2°E, dip angle 12.5°N). The base height of the ionospheric F region over dip equator and a low-latitude station showed similar variation during most of the ESF interval except mainly during 2145–2200 IST (Indian standard time, IST = universal time, UT + 5.5 hours). The zonal electric field variation over dip equator responded to a “prompt penetration” event at ∼2000 IST by gradually changing its polarity from westward to eastward after ∼2015 IST leading to the initiation of ESF at ∼2035 IST. The linear growth rate analysis supports the generation of irregularities only when the eastward electric field owing to the “prompt penetration” effect is taken into account. The zonal electric field became westward again after 2100 IST. However, it ephemerally turned eastward shortly after ∼2145 IST (1615 UT) that is believed to be associated with an “overshielding” condition. A plasma plume got resurrected after ∼30 min indicating the association of the development of this plume structure with the overshielding electric field. The OI 630.0 nm airglow intensity variations observed by a collocated airglow photometer, simultaneously operated in a bidirectional (zenith and east) mode, corroborated well with the ESF structure and dynamics during the disturbed period. These observations evince the active role of interplanetary electric field (IEF) in the development of ESF in the premidnight hours.

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