Horizontal velocity dispersion of medium-scale travelling ionospheric disturbances in the F-region

Abstract

Daytime observations of the horizontal velocity dispersion of medium-scale travelling ionospheric disturbances (TID) near the F2 peak height have been carried out using an array of HF Doppler sounders in central Japan. Cross-correlation analysis of sample records has shown that the horizontal trace velocity is a decreasing function of the period of fluctuations in the range 13.3–40 min. The theoretical dispersion of the atmospheric gravity waves is also calculated using Klostermeyer's (1974) method. Comparison between the observed and the calculated results suggests the possibility that the components of the lower period of the observed velocity dispersion may be a remnant of the quasi-evanescent mode pertinent to lower-height levels.