Find some more high-speed videos of lightning initiated by Gaisberg Tower on YouTube.
On June 14, 2000 during a night storm we captured the first good record of a tower initiated lightning with the high-speed video system. This special camera can record up to 1,000 frames per second with a resolution of 240x512 pixels (8-bit gray values). With a recording time of 1 second the camera detects the overall impact from the initialization process until the last part of flash. For temporal correlation with the measured currents and the ALDIS lightning location records all video images are GPS time stamped. Until 2011, the end of the operation of this camera, some more lightning flashes were recorded. But in most cases the entire mast was covered by the cloud and therefore no clear lightning channel was visible on the video data.
The following video was created from several hundreds of images recorded by high-speed video camera. This Flash, recorded on June 14, 2000 at 20:30 (UTC), shows multiple changes of brightness of the lightning channel caused by current pulses superimposed on the initial continuing current (ICC). Obviously there is a movement of the entire lightning channel from left to right. This displacement of the lightning channel by several meters is a result of relatively high wind speed which prevailed at the time of the impact on Gaisberg.
Analysis of the correlation of measured lightning current and channel brightness on high speed videos showed a linear correlation [Diendorfer et al., 2003]. Based on this finding it is possible to estimate the current components in the individual branches of a video captured discharge.
The figure shows an upward discharge from the Tower with 3 branches. The movie shows that the individual branches do not light up simultaneously, but at different times.
We can only measure the total current at the top of the tower. We can estimate the current components in the individual branches (i1, i2 and i3) from the time variation of the brightness of the different branches.