Doppler frequency fluctuations of lower thermospheric reflections in the equatorial electrojet region

Abstract

The origin of short-period fluctuations from Doppler frequency-shift (P) data is investigated by examining their quantitative relationships with ambient electrojet strength and associated ionospheric conditions. The wave activity from 30-300 s is computed in terms of variations in P as synthesized through reverse FFT. P is found to vary linearly with ambient electrojet strength, and the Doppler fluctuations in the 30-300-s range tend to stop during partial or total counter-electrojet conditions. The highest sensitivity to changes in electrojet strength is noted in the 30-120-s region, and the spectral content of P fluctuations is dominated by the 120-210-s and 210-300-s subbands. The primary source of the short-period fluctuations in P data from the lower F-region reflections near the dip equator is the turbulent state of the diurnal electrojet.