Influence of nonmigrating tides and geomagnetic field geometry on the diurnal and longitudinal variations of the equatorial electrojet

In this study, equatorial electrojets (EEJs) simulated by the Thermosphere-Ionosphere Electrodynamics General Circulation Model (TIE-GCM) were compared with those observed by ground-based magnetometers and the Challenging Minisatellite Payload (CHAMP) satellite. Simulations were performed with or without nonmigrating tidal forcing at the lower boundary and in the frame of the International Geomagnetic Reference Field (IGRF) or dipole field. The model forced by the nonmigrating tides could qualitatively reproduce the local time and longitudinal variation of an EEJ in the frame of the IGRF with accuracy. The tides were important in causing the later local time occurrence of the EEJ peak in the Peruvian sector, and they favored the occurrence of the morning counterelectrojet (CEJ) in the frame of the IGRF. The difference in the EEJ peak intensity between the Peruvian and Indian stations was enhanced due to the tidal effect. The net effect of the tides on the two-station difference was almost doubled in the dipole field compared with that in the IGRF. The TIE-GCM with a tidal input could reproduce a Wavenumber-4 longitudinal structure of the noontime EEJ, but it underestimated the peak EEJ in the East Asia sector. The magnetically eastward electric field and the neutral zonal wind at noontime in theEregion in the TIE-GCM were both weak in the East Asia sector. This model-data discrepancy was at least partly due to insufficient lower boundary forcing in this longitudinal sector.