Abstract:
A comparative study is made on the response of the equator and low latitude ionosphere to three major storms in 2015, namely 17-18 March (St. Patrick’s Day), 22-23 June and 19-20 December, using ionosondes and GPS receivers over the Indian sector. We use observations of foF2 (MHz), h’F (km), equatorial Spread F, L-band scintillations and TEC for this study. As these storms fell on three seasons, the study examines the role of storm-time changes in the composition, winds, waves and electric fields and their interaction with density under these seasons for the occurrence of plasma irregularities and positive and negative ionospheric storms. We noticed positive (negative) storm in December (June) in the main phase. We also noticed positive (negative) storm at the equator (low latitude) during March in the recovery phase. The h’F (km) at the equator is modified significantly by the orientation and magnitude of the storm-time zonal electric field. While the St. Patrick’s Day storm showed an abrupt increase of h′F (km) due to the absence of low latitude Es layers and addition of an eastward electric field to the existing post-sunset enhancement of eastward electric field leading to the generation of severe plasma irregularities and L-band scintillations at wide latitudes, plasma irregularities and scintillations are suppressed during June in the midnight sector due to westward electric field. However, during December, a sudden increase of h′F (km) in the pre-dawn sector caused generation of plasma irregularities. The results further suggest that the ionosphere over India is significantly modified by the storm processes in the night sector during winter due to efficient coupling.
