Response of the equatorial and low-latitude ionosphere in the Indiansector to the geomagnetic storms of January 2005

摘要

The equatorial and low-latitude ionospheric response to three moderate geomagneticstorms (17, 18, and 22 January) during the period from 16 to 23 January 2005 isinvestigated in the context of development/inhibition of the Equatorial IonizationAnomaly (ETA) and the subsequent occurrenceonoccurrence of Equatorial SpreadF (ESF) irregularities on these days. The study is carried out using the Total ElectronContent (TEC) measured with the GPS receivers along the --,80°E longitude sector andthe F-layer bottom height obtained from the Ionosonde located over the dip equatoriallocation of Trivandrum (8.5°N, 77°E, dip latitude '0.5°N) in India. It is observed that, forthe storms on days 17 and 22, the development of the anomaly was inhibited, probablydue to the westward disturbance dynamo electric fields. Subsequently, the post sunsetenhancement in the vertical drift of the equatorial F region was also inhibited significantlycompared to the quiet day pattern and, as anticipated, no ESF was observed on thesedays. A large vertical drift of the equatorial F region followed by nearly simultaneousonset of weak ESF was observed on day 18. The late development of the EIA on this daycould be due to the eastward prompt penetration electric field associated with thesouthward turning of the interplanetary magnetic field. Also, strong and distinct F3 layerappeared for a short time in the morning, reappeared later in the noon time, and thenquickly ascended to the topside ionosphere during the main phase of the storm on day 18.