Classification of CIDs observed in Florida using the lightning detection and waveform storage system(LDWSS)

We analyzed wideband electric field waveforms of 965 compact intracloud discharges (CIDs) that were recorded by the Lightning Detection and Waveform Storage System (LDWSS) operating at the Lightning Observatory in Gainesville (LOG), Florida, during August 2016. The data were acquired for discharges that occurred within 500 km of the LOG. CIDs, which may represent a serious threat to airborne vehicles, were distinguished from other lightning processes using characteristic features of both time-domain waveforms and frequency spectra. Eleven types of CID electric field waveshapes were identified, seven of which have not been reported as separate types before. We found, for the first time, that some CID waveforms may include a slow front or be preceded by a pulse train. More than half of the observed CIDs showed pronounced ringing on the opposite-polarity overshoot of their bipolar electric field waveforms. Only about 1.6% of CID field waveforms had positive initial half-cycle, which corresponds to negative charge moving down, with the overwhelming majority being associated with negative charges moving up. More than half of CIDs were reported by the NLDN as CGs (mostly +CGs), some with inferred peak currents exceeding 100 kA.