Electrodynamics of the formation of ionospheric wave number 4 longitudinal structure

The global wave number 4 longitudinal structure of ionospheric density has been observed recently by a number of satellite measurements and considered as a signature of dynamical coupling from the deep atmosphere to the ionosphere. By using a numerical model of atmospheric electrodynamics with input fields from a whole atmosphere general circulation model and an ionosphere-thermosphere model, we investigated the generation mechanism for the longitudinal structure of the F-region zonal electric field (vertical E x B drift) as a possible driver of the ionospheric density variation, especially with respect to the eastward zonal wave number 3 diurnal tide (DE3) that originates from the convective activities in the troposphere and propagates upward. The simulation showed that the longitudinal profile of zonal perturbation electric field is largely influenced by the zonal DE3 wind around the height of peak Hall conductivity during the daytime, and that it is by the zonal DE3 wind in the F-region during the nighttime. The daytime zonal electric field is a direct result from charge separation induced by the Hall dynamo current, whereas the nighttime zonal electric field is rather produced to satisfy the electrostatic condition.