Tuesday, 13 January 2009: 9:00 AM
Comparison of High-Speed Video and VHF LMA Data for CG Lightning Flashes
Room 131A (Phoenix Convention Center)
High-speed video imaging of cloud-to-ground (CG) lightning flashes at frame rates of 10,000 or more per second are spectacular to view and they lend new insights into lightning processes. By comparing high-speed videos of CG flashes with simultaneous lightning channel maps from a VHF lightning mapping array (LMA), we can gain even further insights into the relationships between visible processes in CG channels and in-cloud processes before, during, and after the CG portions of discharges. On May 7, 2008 we obtained simultaneous 10,000 frame-per-second video data and VHF source location data on four CG flashes. We present an analysis of the data for two of the flashes. Both had clearly visible upward-going leaders in the last video frame before the return stroke. One of them, a single-stroke negative flash, was remarkable in that the return stroke was followed by an extremely long continuing current with numerous M components. It is exceptionally rare for first strokes to be followed by continuing currents. Further, The duration of the continuing current was more than 600 milliseconds, which places it in the less-than-1% frequency-of-occurrence category. During first 300 milliseconds of the long continuing current interval there were 13 M components. Although there were approximatly 3000 VHF source locations in the cloud associated with the flash, very few of them were co-located with the stepped leader, the return stroke, the continuing current, and the M components. There were, however, groups of VHF sources located in the cloud that appeared to be temporally associated with M components. We discuss the activity in the cloud in comparison with the behavior of the visible channel to ground.