HF Doppler Observations of Small Scale Plasma Motions in the Equatorial Electrojet

Recordings of the variations in phase path, P of reflections, at vertical incidence, from blanketing sporadic-E layers over Kodaikanal (dip 3.5?N) revealed small amplitude, quasi-sinusoidal oscillations of 45-180 s periods in the time rate of change of phase path, (Doppler frequency). Geomagnetic micropulsation activity at ground level in the Pc4 range (45-150 s) was not evident at Trivandrum (dip 0.6?S, located ~ 200 km south of Kodaikanal) on all the 26 occasions (out of the total 29 events studied) when geomagnetic data simultaneous with the phase path observations were available. Besides, the short period quasi-periodic fluctuations in were also consistently seen in the data of equatorial sporadic E reflections. We interpret the observed pulsations in as representative of those in the vertical electron drift associated with the longitudinal electrostatic drift waves generated in the equatorial electrojet by the gradient drift plasma instability mechanism.

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