Abnormal Features of the Appleton Anomaly

The equatorial plasma fountain process forms the Appleton anomaly in the F-region ionosphere and is also called the equatorial ionization anomaly (EIA). During this process, the ExB drifts, pressure gradient, and gravity involve removing/diffusing equatorial plasma along the geomagnetic field and dumping it at/around 20° latitudes creating a pair of crests on either side of the magnetic equator. The controlling parameters of the symmetric and asymmetric structure and variability of the Appleton anomaly are not yet well understood. Here, we investigate the abnormal features of the Appleton anomaly and associated phenomena over the American low-latitude regions. These anomalies are also observable using latitudinal profiles of the measured Global Positioning System (GPS)-derived total electron content (TEC) using a network of GPS receivers. The purpose of this analysis is to identify the relative contribution of the possible candidates of the seasonal and day-to-day variabilities/abnormalities of the Appleton anomaly. Such candidates include but are not limited to electric fields, neutral winds, the reverse fountain effect, gravity waves, lunar phases, tides, etc. For this analysis, we used the TEC data collected by ground-based networks of GPS receivers, magnetometers, and Vertical Incidence Pulsed Ionospheric Radar (VIPIR) ionosondes that operated in South America. Similarly, neutral wind data observed from Michelson Interferometer for Global High-resolution Thermospheric Imaging (MIGHTI) onboard NASA’s Ionospheric Connection Explorer (ICON) satellite are employed to examine the abnormal features of the anomalies. To sum up, we discuss the physical mechanisms, drivers, dynamics, and impacts of the abnormal features of the Appleton anomaly in upper atmospheric electrodynamics.