Observation of the neutral-ion coupling through 6-day planetary wave

A westward 6-day oscillation with zonal wavenumber 1 is identified in the global maps of the total electron content (TEC) during May 2003. This signature coincides with wave activities in the mesosphere and lower thermosphere (MLT) region with similar zonal structure and the period, deduced from the temperature and wind observations from the Thermosphere Ionosphere and Mesosphere Electric Dynamics (TIMED) satellite. The vertical wavelength of this 6-day wave is estimated to be ~65 km. The zonal wind perturbations of the 6-day wave maximize in the equatorial region with amplitude of ~30 m/s and the meridional wind perturbations peak at middle latitudes with amplitude of 15-20 m/s. The 6-day oscillation in TEC peaks at the equatorial ionization anomaly (EIA) crests in both hemispheres with a deep minima at the equator. The absolute TEC perturbations maximize at ~1400-1800 LT with amplitude of ~9 (~7) TECU in the southern (northern) hemisphere, which account for ~16% (~10%) of the background TEC. Larger relative TEC perturbations of ~20% are found at 0200-0400 LT. The similar wavenumber-period spectra and the consistent temporal variations of the 6-day periodical signatures in both neutral atmosphere and ionosphere suggest strong neutral-ion coupling through planetary wave.