Equatorial Ionization Anomaly crest magnitude and its implications on the nocturnal equatorial ionospheric plasma irregularity characteristics

Abstract

In this study, the association of Equatorial Ionization Anomaly (EIA) with various post sunset ionospheric irregularity manifestations are brought out empirically using Global Positioning System derived Total Electron Content (GPS - TEC) data from five stations centered around 77° E longitude as well as ionosonde data at a dip equatorial station Trivandrum (geographic latitude 8.5° N ; geographic longitude 77° E) for the days of vernal equinox season of distinct solar activity conditions. The study reveals that the EIA crest magnitude in the evening hours has a direct control on the base height of post sunset ionospheric F- layer (the primary factor responsible for the generation of ionospheric plasma irregularities) on a day-to-day level. Under the condition of strong (weak) EIA crest, the equatorial spread F irregularities are observed to be manifested earlier (later) and are sustained for a longer (shorter) duration. Further, the GPS signal scintillation intensity (quantified by the parameter S4 index) exhibits a direct association with EIA crest strength. This work emphasizes the need to incorporate various EIA features in the current models for better prediction of post sunset ionospheric plasma irregularities which are known to be hazardous for communication and navigation systems.