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

Abstract

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.

Equatorial Spread F structures and associated airglow intensity variations observed over Gadanki

“…However, the reason for the high value of the westward drift is not clear and needs further investigation. Similar such westward velocity on 7 January 2005 was also inferred by Chakrabarty et al (2006) using similar set of observations, when the plasma structures were confined to a limited altitude region around 250-300 km. However, above ∼250 km, the zonal plasma drift is essentially governed by F-region dynamo during nighttime which drives the plasma in the eastward direction.…”

“…In the recent past, comparison between the narrow-band optical measurements of thermospheric airglow emissions and the VHF radar measurements revealed the presence of plasma enhancement (Sekar et al, 2004) extending beyond 350 km and an evidence for fossil bubbles turning active (Sekar et al, 2007) was obtained. In addition, simultaneous triggering of ESF at two zonally separated locations during storm time was identified (Chakrabarty et al, 2006;Sekar and Chakrabarty , 2008) using bi-directional airglow and VHF radar observations. Results obtained with particular ESF structures were discussed in those studies.…”

Identification of active fossil bubbles based on coordinated VHF radar and airglow measurements

“…The nighttime airglow emissions (OI 630.0 nm and 777.4 nm) from thermosphere altitudes (∼250 km and F region peak altitude) have been monitored using a temperature controlled narrow band (0.3 nm) optical photometer whose field of view (3 • ) was chosen to nearly coincide with radar beam width. The details of this photometer (Sekar et al, 2004) and coordinated observations (Chakrabarty et al, 2005(Chakrabarty et al, , 2006 are available in the literature. In addition to these techniques, the layer height movements of the F-region over the dip equator which correspond to zonal electric fields were obtained from the ionosonde observations located at Thumba.…”

“…The background ionospheric conditions near midnight are not conducive, in general, except during some magnetically active times (Chakrabarty et al, 2006) for further development of plasma bubbles. In addition to that, westward electric field during nighttime decelerates the growth of the plasma bubbles.…”

Observations of the F-region ionospheric irregularities in the South American sector during the October 2003 "Halloween Storms"

“…Of the late, the earlier view that a geomagnetic storm suppresses the generation of the ESF is no longer valid (e.g., Tsurutani et al, 2004;Becker-Guedes et al, 2004;Martinis et al, 2005;Chakrabarty et al, 2006). However, several investigators have reported ESF in post midnight period during geomagnetic disturbances earlier.…”