Response of Ionospheric Equatorial Ionization Crests to Lunar Phase

The strength, appearance time, and latitudinal location of the equatorial ionization anomaly (EIA) crest response to the lunar phase are examined using the total electron content of global ionosphere maps during the 18-year period of 2000-2017. The total electron content of the EIA crest reveals semidiurnal tides with 12.42-hr period, while the appearance time and latitude of the EIA crests present prominent semimonthly lunar tides of 14.77-day period. The EIA crests on new/full moon (first/third quarter) lead (lag) those of the overall 18-year average by about 20-40 min, while the EIA crests move the furthest poleward and equatorward 2-5 days after new/full moon and first/third quarter, respectively. Amplitudes of the semimonthly lunar tide in the EIA crest appearance times and latitudes yield the greatest value around perihelion and the smallest value around aphelion, which shows that the solar declination and seasonal effects are important.