First experimental evidence of HF produced electron density irregularities in the polar ionosphere; Diagnosed by UHF radio star scintillations

HF-produced electron density irregularities with scale sizes of several hundred meters were observed in the polar ionosphere by means of UHF-scintillations using the new facilities at Tromso. HF-power densities as low as 20 µW/m² excited irregularities during over-dense (HF < penetration frequency) modification.