Spatio-temporal characteristics of the Equatorial Ionization Anomaly (EIA) in the East African region via ionospheric tomography during the year 2012

Abstract

We present the characteristics of the EIA in the East African sector inferred from ground-based GPS receivers via ionospheric tomography during the year 2012. For the analysis, we developed and used a 2D ionospheric tomography imaging software based on Bayesian inversion approach. To reconstruct ionospheric electron density form slant Total Electron Content (sTEC) measurements, we selected a chain of ten ground-based GPS receivers with stations’ codes and geomagnetic coordinates: ARMI (3.03°S,109.29°E), DEBK (4.32°N,109.48°E), ASOS (1.14°N,106.16°E), NEGE (3.60°S,111.35°E), SHIS (3.26°N,110.62°E), ASAB (4.91°N,114.34°E), SHEB (7.36°N,110.60°E), EBBE (9.54°S,104.10°E), DODM (16.03°S,109.04°E) & NAMA (11.49°N,113.60°E). The temporal, spatial and storm-time characteristics of the EIA and the hourly, day-to-day and seasonal variations of the maximum electron density of F2 region (NmF2) at 15.29°S geomagnetic latitude are presented. We found that the magnitude of the peak and the width/thickness of the EIA pronounced during the equinox and weakened during the solstice seasons at 2100 LT. It is also observed that the EIA persisted for longer time in equinox season than the solstice season. The spatial appearance of the northern and southern anomalies are observed starting from 6.12°N and 10°S respectively along geomagnetic latitude during equinox season. The EIA is localized between 180km and 450km along the altitude during December solstice. The analysis on the NmF2 demonstrated a significant dependence on local time, day and season of the year. We also investigated the storm response of the EIA for the magnetic storm of Day Of the Year (DOY) 274–276. It is observed that the disturbance dynamo related composition change (O/N2 ratio) resulted in a well-developed EIA with an increase in the peak and the width of the EIA at 2100 LT on DOY 275 (main phase of the storm) compared to 274 (initial phase of the storm) and 276 (recovery phase of the storm).