Lunar Tidal Effect on Equatorial Ionization Anomaly Region in China Low Latitude

The equatorial ionization anomaly (EIA) crest derived from GPS observations, F2-layer peak height (hmF2), critical frequency (foF2), and equatorial electrojet (EEJ) in China low latitude are used to study the lunar tidal effect on EIA region for the years from 2006 to 2015. A predominant 14.76-day periodic component in EIA crest, hmF2, and EEJ concurrently appears in some seasonal intervals, which coincides with the half of the lunar revolution period (29.53 days) and the lunar phase, indicating that the 14.76-day periodic oscillation in EIA region is modulated by the lunar tide. This 14.76-day periodic oscillation occurs in all Northern Hemisphere (NH) winter and corresponds to their respective sudden stratospheric warming (SSW) period from 2006 to 2015. In addition, this 14.76-day periodic oscillation also occurs in other seasons for some years, for example, May and August, in which wave power is sometimes comparable to that in SSW period. The occurrence of the 14.76-day periodic oscillation and its wave power during non-SSW seasons in the solar maximum years (2012-2015) is more frequent and higher than that in the solar minimum years (2008-2010). Our results suggest that, besides the NH SSW condition, the solar activity and some other unclear factors are also responsible for the lunar tide enhancement in EIA region.