Plausible effect of atmospheric tides on the equatorial ionosphere observed by the FORMOSAT-3/COSMIC: Three-dimensional electron density structures

The plausible effect of atmospheric tides on the longitudinal structure of the equatorial ionosphere is observed by the FORMOSAT-3/COSMIC (F3/C) constellation during September Equinox, 2006, near solar minimum. The longitudinal structure was first reported in IMAGE satellite airglow observations at the far-ultraviolet (FUV) 135.6-nm wavelength during March Equinox, 2002, near solar maximum. The global three-dimensional ionospheric electron density observed by F3/C shows a prominent four-peaked wave-like longitudinal enhancement in the equatorial ionization anomaly (EIA). The vertical electron density structures observed by F3/C reveal that the feature exists mainly above 250 km altitude indicating that the feature is an F-region phenomenon. The four longitudinal F-region enhancements of the EIA peaks may result from a stronger equatorial plasma fountain at each longitude region produced by a stronger F-region eastward electric field transmitted along the magnetic field lines from E-region where longitudinal variations in atmospheric tides affect the ionospheric dynamo process.