Postsunset equatorial ionosphere under the control of transequatorial neutral wind

The CHAllenging Minisatellite Payload (CHAMP) satellite observes deep plasma depletions around the geomagnetic equator from dusk to midnight. The low electron density is suggested to be linked to two types of Broad Plasma Depletions (BPDs) in literature. Some of the depletions appear with higher F2-layer peak height (hmF2) related to the enhanced upward plasma drift which is known as Pre-Reversal Enhancement (PRE). However, some of them are observed, e.g., at 30° W longitude in July, where the vertical plasma drift is extremely weak or even downward. By evaluating the effects of ion-neutral coupling, i.e., recombination, diffusion and transport, we propose that the transequatorial neutral wind is the main driving force at this place, which controls the equatorial ionosphere hence causes the hmF2 variations and the depletions observed by CHAMP. The neutral wind effect can be particularly important when the electric field-driven dynamics is weak or absent.