Electron precipitation from the inner radiation belt above Arecibo

We examine possible correlations between occurrences of nighttime E-region plasma line (PL) enhancements over Arecibo and 40.75 kHz NAU emissions. On the night of January 1 - 2, 2006, the experiments were conducted from 22: 00 to 6: 00 local time ( LT). NAU transmitter was initially turned off until 01: 45 LT, when continuous operations resumed for the remainder of the experiments. Enhanced PL events lasting < 10 s had central frequencies and bandwidths of about 2.5 and 1.5 MHz, respectively, indicating that Arecibo radar detected 2.3 to 8.5 eV suprathermal electrons streaming along geomagnetic fields. The rate of PL event detections increased by a factor of 2.8 after NAU turn-on. We suggest that 40.75 kHz radiation sporadically leaked though local ionosphere, probably abetted by field-aligned irregularities. The radiation propagated in whistler mode into the L = 1.35 inner radiation belt where gyroresonant interactions with trapped 390 keV electrons increased the precipitation rate.