lightning

[ieatbees]

i have been told recently that lightning doesn't come down but goes up. after the recent storms i couldn't work out if this was the case or not! can anyone help?

[gerkin]

Lightning Sprites go upwards, where Sprites are faint, colorful and exceedingly brief flashes that are now known to erupt high in the atmosphere in a region just below the ionosphere, which begins at an altitude of about 50 miles. Although previously reported by keen-eyed observers, such as airline pilots, sprites have been scientifically documented only in the past decade.

[Clanad]

In addition to the Sprites discussed by gerkin (which I've personally witnessed at 35,000 feet above sea level), we do know that lightning is usually caused by negatively charged electrons migrating to the bottom of a cloud while positively charged ones migrate to the top of clouds (don't know why).  The lower negatively charged electrons make their way, fairly slowly, towards the ground in an effect called stepped leader.  As they approach the ground, they cause a positve charge to occur on something on the ground (wires, T.V. antennas, etc.) If and when conditions are right, a travelling spark is sent from the ground charged object upward, and when the stepped leader and travelling spark meet, voila, lightning occurs... Fairly simple explanation of a complex event.  Lightning also regularly occurs from cloud to cloud without striking the ground...

[Gef]

"Positively charged electrons" - hmmm, so we are talking about anti-matter now.

[Clanad]

Good catch gef... that was a test and you passed superbly.  actuall, bad choice of words.  I should have taken time to explain that positive electrification is due to the deficiency of electrons (compared to the normal number of electrons in a neutral atom).
For example, on rubbing an ebonite rod with fur or cat's skin, the electrons from the cat's skin get transferred to the ebonite rod. The cat's skin now has a deficiency of electrons and so is positively-charged. On the other hand, the ebonite rod has an excess of electrons and hence is negatively-charged.
In the above example, the cat's skin undergoes positive electrification.
Note that it is the electrons and not the protons that get transferred during positive (and negative) electrification. Same holds true in cumulonimbus clouds. 

Thanks!

[Gef]

Lots of info here http://en.wikipedia.org/wiki/Lightning#How_lightning_is_ formed