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

Abstract

Power spectra of the fluctuating component of the east-west electric fields in the postsunset F region at the magnetic equator are presented. The electric fields were derived from vertical plasma drift observations conducted at Trivandrum (dip 0.9° S) by using a HF Doppler radar system. The spectra are found to have spikes, one dominant spike and one or two significant secondary spikes. The dominant spike has period in the range 13-32 minutes and amplitude 5-12 m s^-1. The periods and amplitudes of the secondary spikes are in the ranges 3-10 minutes and 2-5 m s^-1, respectively. The spectra show very little day-to-day variability and have no appreciable changes with geomagnetic activity. 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 in the equatorial postsunset F region.