Simulation of equatorial electrojet magnetic effects with the thermosphere-ionosphere-electrodynamics general circulation model

In this work, the magnetic variations simulated by the NCAR thermosphereionosphere-electrodynamics general circulation model (TIE-GCM) in the vicinity of the magnetic equator are examined to evaluate the ability of this model to reproduce the major features of the equatorial electrojet (EEJ) as observed on the ground as well as on board low-altitude orbiting satellites. The TIE-GCM simulates electric currents of various origins and reproduces their associated magnetic perturbations. We analyze the diurnal and latitudinal variations of the EEJ magnetic effects calculated on the ground in West Africa under approximately the same solar activity condition as in 1993 for the March equinox and June and December solstices. The latitudinal and local time structures of these simulated results correspond well to those that are observed. We also compare longitudinal variations of the midday EEJ magnetic perturbations observed by the CHAMP satellite with the model predictions. Although the simulations and observations both show multiple maxima and minima in longitude, the locations of these extrema often disagree. In the model most of the longitudinal variation of the magnetic variations is associated with nondipolar structure of the geomagnetic field. We find that the modeled contributions of the thermospheric migrating diurnal and semidiurnal tides to the magnetic perturbations have large longitudinal variations, and we suggest that an increase in the amplitude of these tides in the TIE-GCM may cause them to play a major role in explaining the morphology of the EEJ longitudinal variation.