Rocket‐and‐wire triggered lightning in 2012 tropical storm Debby in the absence of natural lightning

Abstract

AbstractLightning Mapping Array source locations, channel base currents, and electric field waveforms are presented for a lightning flash triggered in the rainbands of 2012 tropical storm Debby. The National Lightning Detection Network reported no natural cloud‐to‐ground discharges within 60 km of the North Florida triggering site for at least 20 h before and 8 h after the triggered flash. Additionally, local electric field mill and wideband antenna networks show no close cloud or cloud‐to‐ground flashes. The triggering rocket was launched with negative charge overhead producing an electric field at the ground of 5 kV m−1 and in coordination with X‐band, dual‐polarimetric radar observations of streamers of enhanced precipitation descending from the melting level as they approached the site. The Debby flash consisted of an initial stage (IS) followed by eleven leader/return stroke sequences. The flash exhibited all the processes of normal triggered and natural cloud‐to‐ground lightning: leader/return stroke sequences, continuing currents, K events, and M components. Additionally, the flash exhibited several exceptional characteristics: three return stroke peak currents greater than 25 kA, one very long, 352 ms, continuing current that transferred about 35 C of charge to ground, and a relatively short, 202 ms, IS containing no initial continuous current pulses. Following a near‐vertical upward positive leader attaining 2.8 km height, the IS branched and propagated horizontally at 3.5 km altitude. The flash, exhibiting strokes and continuing current, then ascended to and propagated horizontally at 5.5 km, extending about 25 km south and 15 km east. The 0°C level was near 4.5 km above sea level. It follows from the above that clouds that are not producing natural lightning can represent a triggered lightning hazard to launch vehicles and aircraft.