Wednesday, August 29, 2012


Lightning is tough to model, impossible to predict, and only partly seen. For example, look at red sprites in action: They form above the cloud and go up. There are blue jets as well. Nobody seems to understand how either one works yet.

"When all of these factors are taken together it is not surprising that sprites have been so elusive. However, they can be seen with the unaided human eye." The area around us isn't very suitable for watching for them, but I'll have to try next time I'm out in open land. What you want is dark, dark-adjusted eyes, clear skies to a distant (200 mile) thunderstorm, and something (paper or whatever) to block out the dazzle from the bright lower lightening. Watch above the storm for faint flashes.

There are still lots of hidden and unexpected things not far away.


Assistant Village Idiot said...

We never see things 200 miles away here. When I can see Mt Washington from Mill Hill in Dunbarton, that's less than 100 miles away, and it's a rare occurrence.

From mountaintops we can sometimes see farther, but clouds or haze are usually obscuring visibility somewhere.

james said...

Similarly here. I'd have to go to Blue Mounds to see very far. (Our equivalent of a mountain :-) )

Texan99 said...

I watched a show long ago that claimed that the visible aspect of all lightning strikes started at the ground and went up, and seemed to prove it with slo-mo video. I still find it hard to believe. It sure doesn't look that way in real life. I've often wondered if there was something wrong with that show.

james said...

It makes sense, though. The electric field intensity about a sharp object like a tree or a hill will be larger than that around a blunt object like a thermal layer in a cloud. But what the slow-mo shows is that the ground-up is only the first part, and the cloud down later strikes are bigger and brighter and more frequent. The ground-cloud path is ionized by the first strike, and will keep conducting for a second or so; so the charge from that region of sky and several neighboring sections will tend to drain through that path. I seem to recall the movie showing a fairly faint filament rising, and then another coming down to meet it (and being a little jagged along the way), and then several big cloud down blasts following the original trail.