Modeling Toroidal Currents in the Ionospheric Electrojet Regions

New basis functions, suitable for fitting magnetic field observations of the auroral and equatorial electrojets, are constructed by applying principal components analysis (PCA) to a set of rotated current loops in the ionospheric E-layer. The current loops, which are defined with respect to quasi-dipole coordinates, are placed in the electrojet regions (northern polar, equatorial, and southern polar) and are then rotated and tilted to capture both zonal and meridional flow directions, enabling a fully 2D representation of the toroidal flow in the E-layer. We consider four possible covariance functions that define correlation between individual loops, and use PCA to derive a set of modes representing toroidal electrojet current flow. These modes can be fitted to magnetic field observations recorded in space and/or on ground in order to reconstruct an equivalent height-integrated current system in the E-layer which best describes the measurements. We present an application of this new technique, which we call LoopPCA, to model quasi-steady ionospheric current systems, by fitting mean ionospheric magnetic fields recorded by the Swarm satellite mission over a 6 year time period.