Influence of annual atmospheric tide asymmetry on annual anomalies of the ionospheric mean state

Through respectively adding June tide and December tide at the low boundary of the GCITEM-IGGCAS model (Global Coupled Ionosphere–Thermosphere–Electrodynamics Model, Institute of Geology and Geophysics, Chinese Academy of Sciences), we simulate the influence of atmospheric tide on the annual anomalies of the zonal mean state of the ionospheric electron density, and report that the tidal influence varies with latitude, altitude, and solar activity level. Compared with the density driven by the December tide, the June tide mainly increases lower ionospheric electron densities (below roughly the height of 200 km), and decreases electron densities in the higher ionosphere (above the height of 200 km). In the low-latitude ionosphere, tides affect the equatorial ionization anomaly structure (EIA) in the relative difference of electron density, which suggests that tides affect the equatorial vertical E×B plasma drifts. Although the tide-driven annual anomalies do not vary significantly with the solar flux level in the lower ionosphere, in the higher ionosphere the annual anomalies generally decrease with solar activity.