A POSSIBLE MECHANISM OF THE "SELF-SCATTERING EFFECT" OF POWERFUL HF SIGNALS IN THE IONOSPHERE

Abstract

The paper suggests a possible explanation to the “self-scattering effect” which has been revealed in the experiments on monito- ring the EISCAT heater emissions at three greatly dispersed sites and consisted in synchronous variations in the signal amplitudes and Doppler frequency shifts as observed at all the receiving positions. In particular, numerical simulations have been performed with the use of data from the EISCAT incohe- rent scatter radar which results show that phase path deviations at the upgoing segment of the pump wave trajectory might play the determinative role in producing synchronous variations in the Doppler frequency shifts of the self-scattered signals observed in the experiments. In addition, the characteristics of HF fields scattered in aspect-sensitive directions are determined with allowance for the regular refraction effects in the ionosphere, and a condition for excitation of the ionospheric interlayer duct channel by HF signals aspect-sensitive scattered in a given direction is analyzed. The geometrical optics calculations are made within the Born approximation for an anisotropic power-law model spectrum of random irregularities of the upper ionosphere. It is shown that the suggested mechanism could provide practically identical HF signal scattering characteristics toward all the three receiving sites.