Monday Nov. 26, 2012


Lighning is most commonly produced by thunderstorms (it has also be observed in dust storms and volcanic eruptions such as the 2010 eruption of Eyjafjallajokull in Iceland). 







St. Elmo's Fire (corona discharge) is a faint electrical discharge that sometimes develops at the tops of elevated objects during thunderstorms. 











Here's an actual slow motion movie of a stepped leader.  The video camera collected 7207 images per second ( a normal video camera takes 30 images per second).  The images were then replayed at a slower rate.  A phenomenon that takes a fews tens of milliseconds to occur is spread it out over a longer period of time so that you can see it.









Here's a sketch of one of the best photographs ever taken of an upward connecting discharge.


You can see the actual photograph on the photographers homepage. 





Lightning rods (invented by Benjamin Franklin) make use of the upward connecting discharge.














The figure below shows what we've learned so far in simplified form
 













Here's a stepped leader-upward connecting discharge-return stroke animation.





The image above shows a multiple stroke flash consisting of 4 separate return strokes. There is enough time between separate return strokes (around 1/10 th second) that your eye can separate the individual flashes of light.



When lightning appears to flicker you are seeing the separate return strokes in a multiple stroke flash.  The whole flash usually lasts 0.5 to 1 second.




The latest lightning safety recommendation is the 30/30 Rule.