The PI will focus on high-frequency (HF) radio wave modification of the F-region ionosphere using the upgraded HF facility near Arecibo. He will pay particular attention to fundamental wave-plasma interactions in the ionospheric medium and the use of controlled ionospheric perturbations to elucidate natural aeronomic processes. The research will be timed with the solar sunspot cycle so that experiments can be performed in two distinct ionospheric environments: the nighttime, summer ionosphere (providing a highly stable plasma for controlled experimentation), and the nighttime, winter ionosphere (low collisional loss rates give rise to macroscale temperature/electron density modifications). Basic plasma processes the PI will address include the resonant excitation of Langmuir oscillations and ion waves, so he can fully explore wave-plasma interactions in the 50-ms interaction interval following turn-on of the HF beam in a cold unmodified plasma. He will advance current theories beyond the first 50 ms of modification by investigating how HF-induced plasma irregularities/structures impact wave propagation and altering the evolutionary path of the plasma turbulence. The PI will examine plasma transport phenomena and elastic/inelastic electron collision frequencies in the nighttime ionosphere with HF-induced perturbations. The array of observations this project proposes will be made mainly at Arecibo, but with supplementary processors from GRI.
