On seeding equatorial spread F : Circular gravity waves

A direct link appears to exist between gravity wave (GW) activity in the troposphere and plasma structure in the nighttime equatorial F layer during the solstices. This finding strongly favors a role being played by a neutral‐ion coupling process, which involves (1) a spatially‐varying dynamo current, generated in situ by a GW, and (2) perturbation transfer to the plasma by a polarization electric field. We show, for the first time, how two more of the puzzling features in observed plasma structure, referred to as equatorial spread F (ESF), can finally be explained, if we allow GWs to have circular, instead of plane, phase fronts. These features include (1) early appearance of large‐scale wave structure (LSWS) when the F layer is low, and (2) common appearances of a monochromatic LSWS with a long zonal wavelength.