Identification of the cloud pulse responsible for a trans‐ionospheric pulse pair

Abstract

The Blackbeard VHF radio receiver on the Alexis satellite detects pairs of broadband chirps, each lasting about four microseconds. These chirps are separated by several tens of microseconds and extend in frequency to over 166 MHz. The characteristics of these signals suggest that they are caused by electrical discharges in the Earth's atmosphere, but there is some debate as to whether the discharges occur in the middle atmosphere or within tropospheric clouds. Previously, by comparing the time of the occurrence of these Trans‐Ionsopheric Pulse Pairs (TIPPs) with the occurrence of electric pulses recorded by the National Lightning Detection Network, we have found that they are associated with events classified as positive cloud pulses. Herein we examine one TIPP event that is associated with a near simultaneous (0.75 ms) detection at two stations of the ground network allowing us to determine that the causative event occurred over southeastern Kansas. Knowing the longitude and latitude of the pulse, we show that the interchirp separation time is consistent with the generation of the first chirp of the pair at 8 km altitude followed by the ground reflection of that signal to produce the second chirp of the TIPP.