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Title: Origin of short-period (30-300 s) Doppler frequency fluctuations of lower F region reflections in the equatorial electrojet region
Authors: Sastri, J. H
Ramesh, K. B
Rao, J. V. S. V
Somayajulu, V. V
Keywords: F Region;Doppler effect;Equatorial electrojet;Ionospheric Propagation;Periodic Variations;Plasma Density;Backscattering;Fast Fourier;Transformations;Radar Scattering;Time Series Analysis
Issue Date: Dec-1991
Publisher: American Geophysical Union
Citation: Radio Science , Vol. 26, No.6, pp. 1403 - 1413
Abstract: Measurements of phase path P of lower F-region reflections at normal incidence at Kodaikanal revealed the ubiquitous presence of 30-300-s quasi-sinusoidal variations in the time rate of change of phase path, P (Doppler frequency shift) during day time. A study is made of the influence of the irregularities in the equatorial electrojet on the P fluctuations using simultaneous observations of F-region phase path at Kodaikanal and of equatorial electrojet with the VHF-backscatter radar at Thumba. It is shown that the spectral content of the Doppler fluctuations (quantified in terms of variance, sigma squared computed from P time series synthesized through FFT exp -1 (FFT) in the chosen period bands, 30-300 s/30-120 s of the FFT of original P times series) bears a significant positive linear relationship to the horizontal phase velocity of electrojet irregularities (3-m scale size) on a hourly basis. This result is in consonance with earlier findings (Sastri et al., 1990) of a significant linear relationship of sigma squared to the electrojet strength (estimated from H-field data) and a practical cessation of the P fluctuations at times of disappearance of Esq on ionograms (partial/complete counterelectrojet). The present work substantiates the interpretation that the short-period Doppler-frequency fluctuations are due to phase-path changes imposed on lower F region reflections by the refractive-index variations associated with the convective motions of plasma density irregularities (type I and II) in the daytime equatorial electrojet.
Description: Open Access
ISSN: 0048-6604
Appears in Collections:IIAP Publications

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