Wave-plasma interaction experiments at Arecibo using vertically and obliquely injected HF waves

Summary form only given. In recent ionospheric heating experiments at Arecibo, Puerto Rico, the spectral characteristics of HF enhanced Langmuir waves, among other phenomena, were investigated. Obliquely propagating HF waves were transmitted from a tilted heater in experiments during August 5-11, 1992, while vertically propagating HF waves were employed in experiments during September 17-22, 1992. The cascading spectra of PDI (parametric decay instabilities) produced Langmuir waves were observed in the vertical heating experiments, as expected. Radar measurements of the HF enhanced plasma lines in the oblique heating experiments also showed the excitation of PDI. Theoretical analyses suggest that the VLF waves produced by lightning or injected from a ground-based transmitter near Arecibo can be guided by the HF-induced ionospheric ducts to reach the radiation belts at L = 1.47 and effectively interact with energetic electrons through pitch angle scattering.