HF echoes from ionization potentially produced by high-altitude discharges

Abstract

The presence of ionization associated with high-altitude discharges has been detected using an HF radar operating at 2.2, 2.5, and 2.8 MHz. On several occasions, oblique echoes lasting several hundred ms at night and 1 → 10 s during the day were observed. The echoes turned on in several interpulse times of 70 ms and were generally correlated with strong lightning activity prior to onset. The angles of arrival of sferics detected at three goniometer stations were used to determine the distance to thunderstorms. The data are consistent with specular reflections from columns of ionization produced at 55-65 km altitude and having minimum electron densities of 6×104 - 105 cm-3. The source of the ionization is believed to be high-altitude discharges. Copyright 1997 by the American Geophysical Union.