Postsunset ambient ionization and ionospheric scintillations in the equatorial region under solar activity maximum and minimum conditions

The importance of electrodynamic drift near the magnetic equator in controlling the nighttime ionospheric F region ambient ionization in the equatorial region is examined using ionospheric electron content and VHF scintillation data obtained at Calcutta and ionosonde data obtained at Kodaikanal, India. Both data sets cover the 1977-1986 solar cycle. It is found that the maintenance of high postsunset ambient ionization near the crests of the equatorial anomaly is related to the prereversal enhancement of the electrodynamic drift of the F-region around sunset near the magnetic equator.