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

Abstract

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, Ørsted 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.