Longitudinal Difference of Equatorial Thermospheric Zonal Wind’s Reversal Time and Speed

Based on the Challenging Minisatellite Payload (CHAMP) satellite observations and Thermosphere Ionosphere Electrodynamics General Circulation Model (TIEGCM) simulations, the longitudinal variation of the reversal local time of the equatorial thermospheric zonal wind and its speed at equinoxes during solar minimum period are investigated. It is found that the zonal wind generally turns from eastward to the westward in the morning and from westward to the eastward in the afternoon. However, there are obvious longitudinal differences in the reversal time, with the maximum longitudinal difference of 1.8 h. This is mainly due to the upward-propagating non-migrating tide in the lower atmosphere. The tide can advance the reversal time about 2 h in the afternoon, which is more consistent with the observation. However, it has no obvious effect on the reversal time in the morning, which makes the simulation result different from the observation. The longitudinal wave-4 structure of the zonal wind mainly comes from the non-migrating tide, but the ion drag contributes to the wave-4 structure of the zonal wind. The quantitative analysis shows that the contribution of ion drag to the wave-4 structure is about 25%. The ion drag effect is larger in the daytime than the nighttime, and larger in the frame of the idea dipole field than the real IGRF field.