Spatial structure of auroral day-time ionospheric electron density irregularities generated by a powerful HF-wave

We describe an experiment in satellite radiowave probing of the ionosphere, modi®ed by powerful waves from the HF heating facility at Tromsù (Norway) in May 1995. Amplitude scintillations and variations of the phase of VHF signals from Russian navigational satellites passing over the heated region were observed. We show that both large-scale electron density irregularities (several tens of kilometers in size) and small-scale ones (from hundreds of meters to kilometers) can be generated by the HF radiation. Maximum e€ects caused by small-scale irregularities detected in the satellite signals are observed in the directions sector approximately parallel to the geomagnetic ®eld lines although large-scale structures can be detected within a much larger area. The properties of small-scale irregularities (electron density ̄uctuations) are investigated by applying a statistical analysis and by studying experimental and model mean values of the logarithm of the relative amplitude of the signal. The results indicate that satellite radio probing can be a supporting diagnostic technique for ionospheric heating and add valuable information to studies of e€ects produced by HF modi®cation.