Observations of HF‐enhanced ion waves in the ionosphere

A 138.8 MHz backscatter radar has been deployed at Arecibo Observatory in Puerto Rico to monitor modifications to the ionospheric F region produced by a high‐power, HF (3‐5 MHz) radio wave. This radar provides a new diagnostic tool for examining wave production in the plasma at long (∼ 1 m) wavelengths. When high‐power radio waves are transmitted, strongly enhanced ion‐acoustic waves are detected. The temporal development of the HF‐enhanced ion waves at 138.8 MHz exhibits an "overshoot" behavior similar to that of HF‐induced Langmuir waves and ion waves monitored in the past with the Arecibo 430 MHz radar.