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

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 ionosonde at a dip equatorial station Trivandrum (geographic latitude 8.5° N ; geographic E) for days vernal equinox season distinct solar activity conditions. The study reveals that EIA crest magnitude in evening hours has direct control on base height F- layer (the primary factor responsible generation plasma irregularities) day-to-day level. Under condition strong (weak) crest, spread F irregularities observed to be manifested earlier (later) and sustained longer (shorter) duration. Further, GPS signal scintillation intensity (quantified by parameter S4 index) exhibits strength. This work emphasizes need incorporate features current models better prediction which known hazardous communication navigation systems.