The Naval transmitter, code-named NAU, in Puerto Rico emits radio waves at a power and frequency of 100 kW and 40.75 kHz, respectively. The NAU-generated 40.75 kHz whistler-mode waves are intense enough to excite lower hybrid waves and zero-frequency field-aligned ionospheric irregularities over Arecibo. It is proposed that NAU is responsible for causing the enhanced plasma lines, detected by the Arecibo 430 MHz radar in the nighttime ionosphere F region, in the presence of spread F events. The lower hybrid waves, generated in a broad range of altitudes at the wake of 40.75 kHz whistler-mode waves, have a single frequency of 40.75 kHz but with a spectrum of wavelengths. They can effectively accelerate electrons continuously along the Earth's magnetic field with energies from a fraction of 1 eV to 10 eV. These energetic streaming electrons, when detected by the Arecibo 430 MHz radar, give rise to enhanced plasma lines with a frequency spectrum of ∼3.25-4.75 MHz.
ASJC Scopus subject areas
- Space and Planetary Science