Doppler frequency changes in radio waves propagating through a moving ionosphere

摘要

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−γ amplitude of oscillation in the magnetic field intensity.