FORTE observations of optical emissions from lightning: Optical properties and discrimination capability

[1] Lightning type identification of temporally coincident optical-VHF time series event pairs collected by the Fast On-orbit Recording of Transient Events (FORTE) satellite's photodiode detector (PDD) and VHF instrument allows for the investigation of optical properties as a function of lightning type. General trends in the peak optical irradiance and characteristic pulse widths of PDD-VHF coincident events are studied as a function of lightning type, using previously established techniques to identify lightning type based on VHF spectogram-power time series. While lightning type cannot be identified from optical data alone, there are several notable features in the optical record. The distribution of observed characteristic widths of PDD events has a cutoff near 200 μs, which represents a lower limit on the combination of intrinsic optical emission time and pulse broadening due to photon scattering in the intervening clouds. Events with the highest peak optical irradiances observed at FORTE are typically positive initial return strokes. Also, the median value of peak optical irradiance for cloud-to-ground lightning events is more than double that for in-cloud lightning.