Lunar Tidal Modulation of Periodic Meridional Movement of Equatorial Ionization Anomaly Crest During Sudden Stratospheric Warming

Using the location of equatorial ionization anomaly (EIA) crest derived from GPS observations in China and Brazilian sector, we investigated the longitudinal dependence of periodic meridional movement of EIA crest during sudden stratospheric warming events in 2003, 2006, and 2009. The solar activity was from high to low for the three events. Results show that the locations of EIA crests in both China and Brazilian sectors exhibit obvious and constant 14- to 15-day periodic oscillation being in-phase in two sectors, which coincide with the half of the lunar revolution period (29.53 days) and the lunar phase. The temporal extent of wave power at 14-15 days is consistent with the temporal extent of stratospheric zonal wind, indicating that 14- to 15-day periodic meridional movement of EIA crest is due to enhanced lunar tide modulated by zonal wind. In addition, it is also found that the amplitude of 14- to 15-day periodic oscillation of EIA crest in China sector is larger than that in Brazilian sector, which may be caused by the longitudinal variation of tides and neutral wind pattern.