On wavelike perturbations in the F region

Abstract

Characteristics of wavelike perturbations in the F region are deduced from Doppler measurements made on CW transmissions between time station CHU, Ottawa, Canada, and AFCRL, Bedford, Massachusetts. For periods ranging from 5 to 100 min, occurrence frequencies and phase‐path amplitudes of F‐region perturbations are obtained for the years 1968–1970. While shorter periods are observed to occur more frequently than longer periods, peaks in the distribution are sometimes observed between 10 and 20 min. Amplitude distributions derived from phase‐path undulations, which usually reveal an increase of amplitude with period, are at times found to fluctuate, indicating preferred bands of quasiperiodic activity in the Fregion. For selected ionospheric undulation events, ratios of phase‐path amplitude to wavelength are estimated to be usually less than 0.02, but sometimes 0.05. The spectra of time series, derived from ionospheric Doppler measurements, are obtained by means of Fourier‐analysis and maximum‐entropy methods. These spectra are isometrically displayed using overlapping data windows while advancing in the time domain to observe the dynamics of ionospheric waves. Comparisons are made with comparable data samples derived from random numbers. While both spectral analyses show similar results, the maximum‐entropy method appears to make it more certain that temporal changes of the spectra result from actual changes in the periods of wavelike ionospheric perturbations. For estimating the propagation effects resulting from the overhead passage of several traveling waves, mirrorlike reflection surfaces are synthesized computationally through the superposition of cylindrical waves of different characteristics. For a bistatic radar configuration, their effects on changing ray‐azimuth deviations and Doppler shifts are illustrated.