CASE STUDY: 'Incomplete' tower lightning leaders
: Oklahoma City, Oklahoma - May 7, 2007
OKLAHOMA CITY, OK - The image above is from a 35mm slide (Fuji Sensia 100, 20 seconds @ F8, 28mm lens) taken at the northern Oklahoma City tower farm during thunderstorms overnight on May 7, 2007 (Click image to enlarge). The image shows incomplete upward lightning leaders eminating from the tops of five of the towers in response to a simultaneous large 'anvil crawler' discharge directly overhead.
Complete and incomplete leaders
The initiation of these upward leaders are triggered by an in-cloud lightning discharge above tall towers or skyscrapers. The leaders normally indicate the beginning of a typical ground to cloud lightning flash, but as has been repeatedly chased, some of these leaders terminate prematiruely before reaching cloud base. In most cases chased, the leaders propagate all the way to cloud base and into the cloud while recoil-leader dart-leader initiated return strokes occasionally re-illuminate the channel.
View and sound from simultaneous video
The first lightning discharge shown in the following video clip is the same in the 35mm slide image above. In the video, the leaders are not visible due to the triggering cloud flash overexposing the frames. However, the thunder from the leaders is distinctly heard as several short crackles, separated in time by periods of silence, just before the louder thunder from the anvil crawler itself arrives:
EXPEDITION VIDEO: Oklahoma City tower lightning: Watch Video
The abrupt end of the thunder from the leaders indicates that the leaders terminated in mid-air some distance above the tower tips.
Leader details
The following images are zoomed crops of the original slide, showing each of the five leaders and their termination in mid-air. Notice the upward branching, characteristic of a ground-to-cloud discharge. Click images to enlarge
   
Leader completion to full discharge
The following 35mm slide was taken on the same night at the same location (from a different vantage point). In this slide, the leaders reached cloud base and beyond, resulting in a full-intensity illumination of the channel. The video above also shows this discharge and attendant thunder.
In this instance, the video camera captured one frame showing a leader propagating upward from the tower tip:
In this case, the leader did not terminate in mid air, but reached cloud base and beyond, resulting in a full-intensity illumination of the channel. as shown in the slide above.
Other incomplete upward-moving lightning leaders and thunder sounds
Incomplete lightning leaders have been documented previously, with varying lengths chased. Some leaders are hundreds of feet of length with branching exhibited (as with the above examples), while others are only a few feet in length. All leaders create thunder, but thunder from leaders shorter in length may not be audible to an chaser. The duration of the thunder is a factor of the length of the channel.
Very short 'Incomplete leader' at the WVAH TV tower, St. Albans, WV
MORE READING: Detailed abstract of ground-to-cloud lightning discharges
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