Doppler Frequency Changes in Radio Waves Propagating Through a Moving Ionosphere

Abstract

Doppler frequency changes for a vertically incident and reflected radio wave caused by a redistribution of electrons in the ionosphere due to drift motions set up by an electric field across the earth's main magnetic field are discussed. The Doppler frequency change is given as a linear function of the two horizontal components of the electric field with coefficients which are functions of the relevant ionospheric parameters and the frequency of the sounding radio wave. The Doppler frequency. change can also be given as a function of the intensity of the magnetic variation, provided that a suitable relation can be found between the intensity of the magnetic variation observed on the earth's surface and the intensity of the electric field in the ionosphere. The Doppler frequency change has been given in this way for two cases; one is for a uniform time‐changing magnetic field parallel to the geomagnetic axis which roughly represents the Chapman‐Ferraro field for sudden commencements of geomagnetic storms. The other is for the field due to alternating electric currents in the ionosphere. Several theoretical predictions have been made which can be compared with observations. The amount of the Doppler shift is about 1 c/s in middle latitudes for a 4‐Mc/s sounding wave for a sudden commencement with a time scale of 4 min, and magnitude several tens of gammas. The Doppler shift due to alternating currents in the ionosphere amounts to only 1 c/s for a 4‐Mc/s radio wave with a 50‐y amplitude of oscillation in the magnetic field intensity.

Observations of Pc 3-4 and Pi 2 geomagnetic pulsations in the low-latitude ionosphere

“…The ®rst attempts to model the coupling of geomagnetic ®eld¯uctuations to the ionospheric plasma were by Rishbeth and Garriott (1964) and Jacobs and Watanabe (1966). Poole et al (1988) showed that for downgoing transverse Alfve n mode waves three mechanisms contribute to the ionospheric Doppler oscillation.…”

Sudden frequency deviations due to immediate effect of geomagnetic sudden commencements.

“…However, the correlation between the amplitudes of the positive spike and the amplitude of the SC reported by HUANG et al (1973) has not been noticed in our data. It is to be emphasized that our results pertain to observations over two long radio propagation paths of different lengths (1290km and 5700km) while HUANG et al (1973) used data for one short propagation path JACOBS and WATANABE (1966) theoretically investigated the relation between Doppler frequency changes and sudden commencements for vertically insident and reflected radio waves. A comparison of our results with those predicted by JACOBS and WATANABE (1966) using the equivalence theorem for frequency deviations could not be made due to lack of electron density profile data necessary to fix the angle of fire using ray tracing procedures.…”

ULF wave occurrence statistics in a high-latitude HF Doppler sounder

“…Fenwick and Villard (1960) ®rst suggested that changes in the Earth's magnetic ®eld were associated with observed shifts in the frequency of HF radio signals. Since then, short period oscillations of HF wave signal frequency have been correlated with magnetospheric ULF pulsations (which have periods in the range 0.1 s to 600 s) measured by ground magnetometers (e.g Jacobs and Watanabe, 1966;Klostermeyer and RoÈ ttger, 1976;Menk, 1992). For a more detailed description of the Doppler technique see Georges (1967) and for a discussion on its application to observing ULF waves see Wright et al (1997).…”