Longitudinal variation of the E-region electric fields caused by atmospheric tides

Polarization electric fields created by the E- and F-region dynamos cause the uplift of F-region plasma. The subsequent redistribution of that plasma along the magnetic field lines creates the equatorial ionospheric anomaly (EIA). Observations of the post-sunset EIA made by the IMAGE and TIMED satellites are compared here with CHAMP, Orsted and SAC-C observations of the noontime equatorial electrojet (EEJ). During magnetically quiet periods around equinox, the EIA and EEJ show a remarkably similar four-peaked wave-like longitudinal variation. Its structure is consistent with the longitudinal variation in the strength of diurnal tides that drive the E- region dynamo. This indicates a strong vertical coupling between the ionosphere and troposphere because the four-peaked tidal structure is driven by tropospheric weather. Furthermore, the dayside ionospheric conditions are found to perform the global-scale longitudinal structure of the post-sunset ionosphere at low latitudes.