Global Longitudinal Dependence Observation of the Neutral Wind and Ionospheric Density Distribution

The statistical global view of the low-latitude ionospheric density stimulates further interest in studying the strong longitudinal variability of the ionospheric density structures in low-to-equatorial latitudes. However, we are not completely certain how the electrodynamics and ion-neutral coupling proceeds at low latitudes; in particular, the longitudinal difference in the dynamics of plasma structures in the low-to-mid latitude ionosphere is not yet fully understood. Numerical studies of latent heat release in the troposphere have indicated that the lower atmosphere can indeed introduce a longitudinal dependence and variability of the low-latitude ionosphere during quiet conditions. For the first time, we present simultaneous observations of the tidally modulated global wind structure, using TIDI observations, in the E-region and the ionospheric density distribution using ground (global GPS receivers) and space-based (C/NOFS in situ density and GPS TEC on CHAMP) instruments. Our results show that the longitudinally structured zonal wind component could be responsible for the formation of wave number four pattern of the equatorial anomaly. 1. Introduction The plasma in the low-latitude ionosphere between ±30° magnetic latitude exists entirely on closed field lines and so is relatively cut off from magnetospheric and solar-wind drivers compared to mid- and high-latitude regions of the ionosphere. Most frequently, the highly populated plasma density in this region, which may be about two-thirds of all of the plasma in geospace, can become a disturbed space environment and disrupt the detection and tracking of aircraft, missiles, satellites, and other targets, distort communication and navigation, and interfere with global command, control, and surveillance operations. The plasma in the low and equatorial latitudes is disturbed or redistributed by transport mechanisms that form enhanced density located several degrees to either side of the magnetic equator, forming the equatorial ionization anomaly (EIA). The vertical drift (primarily drift) is the primary plasma transport mechanism at low-to-equatorial latitudes. There are few cases reported on the night side [1, 2] as the EIA formation process is predominantly active on the dayside. In the evening sector, when the conductivity becomes stronger at the terminator, the plasma redistribution is intensified again, forming a stronger EIA structure known as the prereversal enhancement. The redistribution of plasma occurs both during disturbed and quiet periods. During magnetically quiet periods, the tidal