Broadband Interferometry Analysis of Geostationary Lightning Mapper Events

The Geostationary Lightning Mapper (GLM) onboard the recently launchedGOES-16 satellite provides near real-time optical lightning observationsfor much of the western hemisphere. Of significant interest is whattypes of lightning discharge processes are being detected, thecharacteristics of those discharges and the detection efficiency forthem. A VHF broadband interferometer, in conjunction with a fastantenna, can detect, classify and 2D-map a wide range of dischargeprocesses at a level of detail which is unmatched by any otherinstrument. A VHF broadband interferometer system was operated at theKennedy Space Center (KSC) between mid-February and early July of 2017as part of the GLM Cal/Val field campaign. The KSC Lightning MappingArray (LMA) collected 3D flash data which was combined withinterferometer data for some flashes to gain additional insights intoGLM detections. Another broadband interferometer system will beoperated at Langmuir Laboratory starting in early August of 2017.Analysis of GLM events shows that they are composed primarily of 3different discharge processes: initial breakdown pulses (IBPs), negativestepped leaders and K-changes. The detection of stepped leaders tendsto occur when they are not far from cloud top, consistent with theresults for prior space-based sensors in low earth orbit [Thomas et al.,Geophys. Res. Lett., 27, 1703, 2000]. Similarly, the K-changes whichare detected tend to be those which propagate into the upper levels of abilevel intracloud flash. There also is significant storm-to-stormvariability in the frequency, characteristics and detection efficiencyof these and other discharge processes. Such variability can be animportant consideration when applying GLM data to now-cast severeweather events, produce regional lightning density maps and more.