Swarm equatorial electric field chain: First results

Abstract : The eastward equatorial electric field (EEF) in the E region ionosphere drives many important phenomena at low latitudes. We developed a method of estimating the EEF from magnetometer measurements of near-polar orbiting satellites as they cross the magnetic equator, by recovering a clean signal of the equatorial electrojet current and modeling the observed current to determine the electric field present during the satellite pass. This algorithm is now implemented as an official Level-2 Swarm product. Here we present first results of EEF estimates from nearly a year of Swarm data. We find excellent agreement with independent measurements from the ground-based coherent scatter radar at Jicamarca, Peru, as well as horizontal field measurements from the West African Magnetometer Network magnetic observatory chain. We also calculate longitudinal gradients of EEF measurements made by the A and C lower satellite pair and find gradients up to about 0.05 mV/m/deg with significant longitudinal variability.