Small-amplitude, short-period waves in the E and F regions of the ionosphere

Abstract

ACCURATE measurements of the virtual height of radio waves reflected from the ionosphere have been made by using a phase path ionosonde¹. This instrument determines the virtual height, h′, from the variation of echo phase with frequency, ϕ(f), since h′ = (c/4π)(∂ϕ/∂f). Measurements are made in two ways. First, the ionosonde is swept in frequency and h′ determined by taking the Fourier transform of the phase measurements on a number of frequencies. This is a form of pulse synthesis and very narrow pulses may be synthesised by combining measurements over a relatively wide frequency range¹. The second mode of operation is to repeatedly step the ionosonde through 20 frequencies in 0.4 s so that detailed time variations and height structure can be measured. Provided there are no overlapping echoes, virtual heights can be calculated by determing ∂ϕ/∂f from adjacent frequencies. Suitable choices of frequency intervals can give very accurate values of h′ (ref. 2). This paper presents results which show that small-amplitude (< 500 m peak to peak), short-period (∼ 10s) waves can occur in the E and F regions of the ionosphere.