Six-Day Periodic Variation in Equatorial Ionization Anomaly Region

Using the location of equatorial ionization anomaly (EIA) crest derived from GPS observations and CHAllenging Minisatellite Payload (CHAMP) satellite measurement, along with the F2 layer peak height (hmF2), critical frequency (foF2), and the equatorial electrojet (EEJ) in India and China longitudinal sectors, we found the obvious 6-day oscillation in these ionospheric parameters during 16 April to 31 May 2003 and 21 September to 26 October 2004. The tidal amplitudes of EEJ are enhanced during the positive phase of the 6-day waves and are weakened during its negative phase. Since the strong 6-day planetary wave activities in mesosphere and lower thermosphere (MLT) region during these two events have been reported by earlier studies, this 6-day oscillation in EIA region can be due to the interaction of enhanced planetary waves with the tidal wind. Moreover, the temporal variations of this 6-day wave are consistent and in phase in these ionospheric parameters, indicating that the 6-day planetary wave modulates electric fields via E region wind dynamo, thereby altering the vertical height and horizontal distribution of electron densities through upward E x B drift, which results in the periodical variations in these ionospheric parameters in F region. These observation results provide insight into how the 6-day planetary waves modulate the ionospheric morphological structure.