Equatorial and low-latitude ionosphere-thermosphere system response to the space weather event of August 2005

Abstract

[1] The response of the equatorial and low-latitude ionosphere-thermosphere system to the geomagnetic storm during 23–26 August 2005 is investigated. The study is carried out using the vertical total electron content (VTEC) measured by GPS receivers along the 77–78°E longitude and the O/N2 ratio obtained from the Global Ultraviolet Imager instrument on board the TIMED satellite. The equatorial ionization anomaly (EIA) shows a poleward latitudinal expansion on 24 August, probably associated with an eastward prompt-penetration electric field. The equatorial and low latitudes show an increase in VTEC during the main phase of the storm on 24 August. The prompt-penetration eastward electric field, along with an increase in the O/N2 ratio, could be responsible for this observed positive phase. The VTEC variations on 24 August also reveal the signature of a large-scale acoustic gravity wave/traveling atmospheric disturbance propagating with a horizontal velocity of ∼750 m/s. Suppression of the EIA is observed during the storm recovery phase on 25 August, which probably is associated with the westward disturbance dynamo electric field and the equatorward expansion of the neutral composition changes (O/N2 depletion).