Posts Tagged high-speed camera
We know from observation and analysis of horizontally extensive lightning flashes that often negative leaders travel horizontally through a layered positive charge region that spans large areas. We frequently observe that positive cloud-to-ground return strokes occur along the path the negative leaders travel but in trail of the negative leader tips. Current thinking is that the negative leaders become cutoff from their original positive ends and then develop new positive leader ends that propagate downward to the ground and cause a +CG return stroke that then further extend the negative leaders. Although we have frequently documented the positive leaders growing toward ground after negative leaders propagate in cloud, due to the clouds, we rarely are able to see the positive leader development initially take place from the previously formed negative leader channel. This video contains three cases where we see the negative leader channel from which a new positive leader develops, propagates to ground and causes a +CG return stroke that travels toward the end of the negative leaders, thus furthering their propagation. What is interesting and has yet to be understood is how the positive leader seems to develop from a still luminous negative leader channel segment. The luminosity in the negative leader channel suggests it is still actively carrying current and not completely cutoff. Therefore, we need to determine through further research the mechanism by which a positive leader is able to form and develop from this luminous channel. This behavior was first documented and described in a paper by Saba et al., 2009 using high-speed camera imagery.
Saba, M. M. F., L. Z. S. Campos, E. P. Krider, and O. Pinto Jr. (2009), High-speed video observations of positive ground flashes produced by intracloud lightning, Geophys. Res. Lett., 36, L12811, doi:10.1029/2009GL038791.
This is one of the best positive cloud-to-ground flashes that I have filmed. When you watch the video remember that lightning leaders grow as bidirectionally with a positive and negative end. We see the positive leaders of this flash below cloud base and the negative end of the leader network is higher up in the clouds and therefore not visible. There are two sets of positive leaders to focus on. The farther leaders are on the left descending to ground and the right positive leaders closer to the camera spread out horizontally along cloud base. Once the far positive leaders reach ground a return stroke occurs. Once the return stroke traverses the leader network, the connected channel grows as an upward propagating negative leader higher up in the storm. The closer leaders also have a negative end that is growing unseen in the upper part of the storm but these leaders do not connect with ground and continue to spread out horizontally. Frequently, some of the positive leader branches become cutoff and develop fast moving bidirectional recoil leaders that attempt to reionize the decayed positive leader branches. The negative end of the recoil leaders travel toward the negative end of the flash by racing toward the place where the positive leaders emerged below cloud base. This continues for quite some time. You may consider this to be a hybrid flash with a ground flash component (farther) and an intracloud flash component (nearer) both raising negative charge upward toward a positive charge region. This flash was filmed at 5,600 images per second.