Recent advances on equatorial spread F

Equatorial spread F (ESF), a manifestation of the plasma instabilities in the F region of the equatorial ionosphere, has been a subject of active study for well over five decades. The early phase of ESF studies, based mainly on ionosonde data, was concerned primarily with the morphological description and statistical characterization of the phenomenon. The application of high power VHF/UHF radar, rocket and satellite techniques, coupled with theoretical and numerical simulation studies, marked the beginning of a new phase of studies providing a physical insight into the plasma instability processes governing the onset and evolution of the ESF. The experimental and theoretical developments in the field having been covered in earlier reviews, for the most part, the scope of this paper is limited to an overview on the recent advances on ESF of current interest. The aspects dealt with, in particular are: effects of vertical wind and electric field on the evolution of ESF, gravity wave seeding of ESF, updrafting and downdrafting of plasma bubbles associated with ESF and the role of steepened structures and drift waves in the development of ESF