Evolution of Langmuir turbulence and stimulated electromagnetic emissions excited with a 3‐mHz pump wave at Arecibo

Abstract

We present the results of a comparative experimental study at Arecibo of the initial temporal development of stimulated electromagnetic emissions (SEE) and HF‐enhanced plasma lines (HFPLs) excited in the ionospheric F region by a high‐power O mode radio wave at 3.1745 MHz. These results show that the portion of the SEE spectrum which extends from approximately −30 kHz to +10 kHz in the sidebands around the injected HF wave, and which is usually referred to as the narrow continuum SEE component, exhibits an overshoot behavior very similar to that of the upshifted HFPL of the 430‐MHz radar. Over timescales of a few hundred milliseconds, the narrow continuum emission weakens at all frequencies and gradually changes shape to become more structured. At 3.1745 MHz the amplitude of the HFPL is significantly smaller than that observed at higher HF frequencies; after an overshoot period of 300–500 ms, the HFPL often disappears completely.