Spectra of the AC electric fields in the post-sunset F-region at the magnetic equator

Abstract

Power spectra of the fluctuations in the East-West electric field in the post-sunset F-region at the magnetic equator (determined from vertical plasma drift measurements) are presented. The spectra reveal that the fluctuations consist of several components with periods varying from a few minutes to several tens of minutes. The dominant fluctuations have periods of the order of a few tens of minutes with the most frequent being about 30 min; the periods show no dependence on the level of magnetic activity. The spectra also indicate that one component of the fluctuations, usually the component with period about 30 min, is amplified during the period of the upward drift enhancement and attains maximum amplitude at around the time of the evening downward reversal. In general, the fluctuations have minimum amplitude at around 22:00 local standard time (L.S.T.). The characteristics of the spectra suggest that the frequently occurring medium scale gravity waves could be a source for the observed fluctuations in the East-West electric fields.