Simulated wave number 4 structure in equatorial F-region vertical plasma drifts

This article investigates the wave number 4 longitudinal structure in equatorial vertical E x B plasma drifts (V-perpendicular to), using the Theoretical Ionospheric Dynamo Model, Institute of Geology and Geophysics, Chinese Academy of Sciences, Version II model and the DE3 tide wind from the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED)/TIMED Doppler interferometer (TIDI) observations. We simulate this longitudinal structure and examine its intra-annual variations and the effect of different DE3 tide components and of different current components on it. We find that this longitudinal structure shows obvious intra-annual variation, being strongest in northern summer and autumn and weakest in northern winter. This result is consistent with the intra-annual variation observed by Ren et al. (2009b). Our simulations also suggest that the eastward propagation of the DE3 tide can cause the eastward shift of the wave number 4 structure in V-perpendicular to. The wave number 4 structures in V-perpendicular to are mainly driven by a zonal wind component of DE3 tide, which contributes much more than the meridional wind component of DE3 tide to the wave number 4 structure in V-perpendicular to. With the influence of the coupling of ionospheric electric fields along the highly conducting magnetic field lines, the symmetric wind component of DE3 tide plays a more important role in the wave number 4 structure in V-perpendicular to than the antisymmetric component does. The intra-annual variations of the wave number 4 structure in V-perpendicular to are mainly controlled by the symmetric wind component of DE3 tide. Our simulations also suggest that the wave number 4 structures in V-perpendicular to are mainly driven by the Hall current.