88th Annual Meeting (20-24 January 2008)

Tuesday, 22 January 2008: 1:30 PM
Visualization of Naturally produced lightning strikes using high speed imaging
222 (Ernest N. Morial Convention Center)
Timothy M. Samaras, Applied Research Associates, Inc., Littleton, CO; and W. A. Lyons
During the Summers of 2006 and 2007, the author organized/performed a field experiment to collect high-speed imagery of naturally produced lightning strikes. This innovative approach used current state-of-the-art digital high speed imaging equipment. Included was a modified Beckman and Whitley (B&W) 192 with 82 11-megapixel imagers in place of film to provide high resolution/high dynamic imagery at a speed of 1,000,000 pictures per second.

The purpose of the field experiment is to use ultra high-speed photography to visualize a naturally produced cloud-to-ground lightning strike. The collected imagery will be used to illustrate and investigate some of the basic physical processes of lightning (R. Thottappillil, 2005):

1. The initial breakdown process

2. Lightning stepped leader and dart leader

3. Lightning attachment to objects

4. Lightning return stroke

During the Summer of 2006, the author captured several hundred digital files of the stepped leader/return stroke process using a high-speed imager that is capable of 10,000 frames per second. One of the images captured in 2007 revealed unusual phenomena in the 200 msec before the stepped leader visibly formed. These phenomena consisted of extremely short duration, rapid flashes of visible electrical discharges likely related to initial breakdown processes. A few of these discharges persisted longer than 200 microseconds, while 20% were less than 63 microseconds.

The planned 2007 field trip in New Mexico during the “monsoon” season (August and September) will use the modified B&W to image the attachment process of the stepped leader/dart leader to the return stroke. The author will include these field results in the presentation.

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