Analysis of the Day Side Equatorial Anomaly

• Main Author: Shankar, Jayaprabha
• Format: Others
• Published: DigitalCommons@USU 2007
• Subjects: Day Side; Equatorial; Anomaly; Electrical and Computer Engineering
• Online Access: https://digitalcommons.usu.edu/etd/266; https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=1271&context=etd

Equatorial Ionization Anomaly (EIA) is a region of peak plasma density found at ± 10 ◦ to 20 ◦ magnetic latitudes at F-region altitudes. In 2002, NASA launched the Global Ultra Violet Imager (GUVI), which can observe the EIA at various local times, longitudes, and seasons by the glow of the recombining electrons and ions in the plasma. This thesis presents the observations of the geomagnetic quiet time EIA and its global behavior at all local times using 1356 ˚A radiance data from high altitude GUVI limb scans. Limb data is prepared for analysis using reduction techniques that remove from the limb file, contaminating signatures of stars, glints, and low altitude day time neutral atmosphere emissions. A simple comparison of the subtracted data at different local times, longitudes, seasons, and magnetic activity reveals significant EIA variability with each of these factors. A global morphology of the quiet time EIA is developed using metrics such as the peak latitude and peak radiance, extracted from the EIA structures. The study shows that the EIA develops gradually in the day, peaking between 1100 to 1400 hours LT, and falls in the night time. Signatures of the prereversal drift enhancement due to enhanced post-sunset F-region vertical drifts appear during December solstice seasons between 19:00 to 21:00 local time. The GUVI EIA observations are compared with 1356 ˚A radiance data simulated from electron densities predicted by ionospheric models, namely USUGAIM and TIMEGCM. Results show that the models overestimate the radiance values by a small amount. However, the EIA variability with local time and longitudes as predicted by the models compares well with the GUVI observations.