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 full ground to cloud lightning discharge, but as has been repeatedly observed, some of these leaders do not make it all of the way to the cloud discharge already in progress. In most cases observed, the leaders propagate all the way into the cloud, resulting in full return strokes as the charge areas and/or existing in-cloud lightning channels are contacted.
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 parent anvil crawler 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.
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. Had the leaders been able to reach into the cloud, their channel paths would have carried high current in the form of bright return strokes. 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, a full ground-to-cloud lightning discharge is occuring to one of the towers. 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 continued into the cloud and completed a full discharge sequence 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 observed. 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 observer. 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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