High-power high-frequency-induced Langmuir turbulence in the smooth ionosphere at Arecibo. II. Low duty cycle, altitude-resolved, observations

This is the second of two papers comprising a theoretical and observational study of new, altitude-resolved, observations at Arecibo of Langmuir turbu lence induced in the ionosphere by a new, more powerful, high frequency hea ter operated at very low duty cycles. Altitude resolution of 150 m in incoh erent scatter radar spectra is made possible by the coded-long-pulse method . Here we present the first observation at Arecibo of the well-developed pa rametric decay instability and the Langmuir decay instability cascade featu res in the Thomson scatter radar power spectrum, of the plasma line, at the unmodified matching altitudes under near-cold start conditions. The depend ence of the plasma line spectra on altitude, pump power, and density scale length have been studied. The temporal growth and saturation of the spectra during heating and the decay of the spectra in the afterglow of heating ha s also been studied in detail. Comparisons are made here with the theoretic al predictions of the companion paper I [DuBois , Phys. Plasmas 8, 791 (200 1)]. From these comparisons and a comparison with recent observations at bo th Arecibo and Tromso, we conclude that all the predictions of modern Langm uir turbulence theory for the radar spectral signatures of the turbulence i n a smooth ionosphere have now been verified. (C) 2001 American Institute o f Physics.