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                   Saturday, August 8, 2009 - 11:05PM

Perseids, Discovery 'Raging Panet', Flickr

By DAN ROBINSON
Editor/Photographer
25 Years of Storm Observing
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Again, it's feast or famine this week. I had planned to do a few full moon images along with starting to go out for overnight Perseid meteors, but we've had cloudy skies and dense fog every night since Tuesday. The tower lightning bonanza on Tuesday was an unlikely oasis of storm action, as it's been otherwise pretty dull so far this month for any type of photography. The upcoming week doesn't look great for observing the meteor shower's peak - with an unsettled weather pattern most every day, IE, no strong sign of clear skies. I don't expect great storm action here with any of this, however - as most likely we'll see remnant cloudiness from storms to our northwest - killing our daytime instability and clouding over our nights. Nonetheless, I think there may be a day or two when we clear out in the evenings, allowing for at least a few hours of Perseid shooting. No real way to forecast that other than just see what's happening each late afternoon. And there's always the chance that the pattern will hit a 'sweet spot' and give us some nice nighttime storms - something to keep an eye out for.

Discovery 'Raging Panet' airs Sunday

Some of my high-definition Pittsburgh lightning footage has been licensed to appear in a show titled 'Raging Panet: Lightning' airing on Sunday night on the Discovery Channel at 10PM eastern (a show on tornadoes airs at 9PM, which also should be good). Apparently the Pittsburgh footage is already running in promos now, though since I don't have cable at my house, I haven't seen it. Should be an interesting program - there will even be a segment on upward lightning during the show.

Trying Flickr

The internet is ever-changing, and one's marketing strategy has to keep up. After carefully reviewing their terms of use/copyright specs, I decided it was safe to upload a set of my (well watermarked) photography on Flickr. My photostream page is here.

Video grabs from Tuesday's lightning

Here are a couple of video grabs from Tuesday's lightning shoot at the tower. These show more of those little upward leaders that appear on many of the discharge's return strokes. I managed to get one still image of these on Tuesday (image here) and again on June 3 of last year (here and here). In case you missed the description from last time, the black mass blocking half the frame is my umbrella shelter that shifted in the wind - ruining most of the video from the shoot. At least it got these little details!

My theory on why these little leaders appear is this. As you can see in the video, the lightning channel moves laterally with the wind at a pretty good rate, depending on how fast the wind is blowing. Most of the time the channel drifts sideways what appears to be over 15 to 30 feet through the course of the discharge! The faster the wind speed, the farther the channel drifts. The only time this doesn't happen is if there is no wind (very rare during a storm). This results in the lower few feet of the channel getting 'stretched' as the rest of the channel moves away from the tower. As long as there is current flowing through the channel, it will simply grow as it is stretched. If the current flow stops (in between return strokes), the channel stretching will cause it to 'break' - creating a gap (5 to 20 feet long) that the next dart leader / return stroke must breach with new leader propagation. The new propagation is apparently bi-directional, with these little leaders being the upward component. They don't happen with every return stroke, but from video it appears that they happen on at least half of them.


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