Longitudinal and seasonal structure of the ionospheric equatorial electric field

The daytime eastward equatorial electric field (EEF) in the ionospheric E-region plays an important role in equatorial ionospheric dynamics. It is responsible for driving the equatorial electrojet (EEJ) current system, equatorial vertical ion drifts, and the equatorial ionization anomaly. Due to its importance, there is much interest in accurately measuring and modeling the EEF. In this work we propose a method of estimating the EEF using CHAMP satellite-derived latitudinal current profiles of the daytime EEJ along with Delta H measurements from ground magnetometer stations. Magnetometer station pairs in both Africa and South America were used for this study to produce time series of electrojet current profiles. These current profiles were then inverted for estimates of the EEF by solving the governing electrostatic equations. We compare our results with the Ion Velocity Meter (IVM) instrument on board the Communication/Navigation Outage Forecasting System satellite. We find high correlations of about 80% with the IVM data; however, we also find a constant offset of about 0.3 mV/m between the two data sets in Africa. Further investigation is needed to determine its cause. We compare the EEF structure in Africa and South America and find differences which can be attributed to the effect of atmospheric nonmigrating tides. This technique can be extended to any pair of ground magnetometer stations which can capture the day-to-day strength of the EEJ.