Non-migrating Tidal Influences on Longitudinal Structure of the Topside Ionosphere
Abstract:Recent evidence suggests that atmospheric tides can be significant drivers of the global ionospheric structure, especially at low latitudes. In particular, a wavenumber-4 (WN4) pattern has been observed in several parameters including total electron content (TEC), zonal winds, [O]/[N2] ratio, distribution of NO, the equatorial electrojet current density, and ion density. WN4 is thought to be a signature of the DE3 non-migrating tide, which originates in the troposphere and modifies the E-region electric field and equatorial ExB drifts, in order to re-distribute plasma at higher altitudes.
We present ionospheric measurements by DMSP showing longitudinal variations at low latitudes. Monthly averages of evening ion densities often clearly show a WN4 or WN3 pattern along the magnetic equator, although these patterns are not always consistent on a day-to-day basis. We examine how the WN4 pattern at DMSP altitudes varies across local time, season, and solar activity, and interpret these variations in terms of tides, composition, and field-aligned transport.