Effects of geomagnetic pulsations on the Doppler shift of HF backscatter radar echoes

The effects of geomagnetic pulsations on the Doppler shifts of HF backscatter radar echoes are studied. Three mechanisms are considered: (1) variation of the phase refractive index under the influence of the varying magnetic component, (2) modulation of the plasma density, and (3) electrodynamic drift of the ionosphere. It is shown that the electrodynamic drift is probably the most efficient mechanism to account for the measured Doppler shifts. In this model the Doppler shift on F propagation modes is sensitive to the eastward electric field of the wave, while E propagation modes are sensitive to the northward and eastward components with weights depending on the reflection height. Pi 2 and Pc 3 effects on the Doppler shift of backscattered echoes are presented in the experimental part. In one example of continuous pulsations it is found that the coherence of ground magnetic variations and HF echo Doppler shifts is high near specific frequencies in the spectra. The coherence of radar measurements in resolution cells about 100 km apart is nearly unity and the cross‐phase spectra show very small phase differences. An example of the effects of Pi 2 pulsations on F and E s propagation modes is presented.