Simultaneous observations of the electron density and the zonal wind obtained by the CHAMP satellite at 400 km are used to study systematic longitudinal variations. The time period selected is August–September 2004 allowing observations at pre-noon and post-sunset hours. The equatorial ionization anomaly (EIA) and the zonal delta-wind (deviation from zonal average) show a persistent and dominant 4-peaked longitudinal variation. We interpret this structure as caused by the wavenumber-3 nonmigrating diurnal tide (DE3). The EIA and the zonal delta-wind exhibit extrema at about the same longitudes. But, while the intensifications of the EIA and the delta-wind are in phase during the evening hours, they are out of phase in the morning. Possible coupling mechanisms are investigated.