3
$\begingroup$

It's easy to find explanations of the theories of charge accumulation in clouds during storms, as well as ones describing suspected processes leading to lightning channel formation. What I have yet to encounter is any theory describing how a large region of a cloud can be conductive enough (for any duration, long or short) to allow charges to be conducted into a lightning bolt channel.

In other words, how would the ice or water particles that supposedly collect charge move these charges toward a strike channel without some kind of conductive plasma between them? Is there plasma that reaches into large cloud regions? If so, how does it form and what might be the lifetime?

$\endgroup$
  • $\begingroup$ It's not that the cloud becomes conductive, it's that it's a big insulator which allows for the accumulation of charge in regions. If the clouds were insulators, they would almost never discharge through lightning because charge would never accumulate enough to breakdown the atmosphere. $\endgroup$ – honeste_vivere Jun 11 '18 at 13:33
  • 1
    $\begingroup$ @honeste_vivere, I'm assuming you meant 'If the clouds were conductors ...' ... $\endgroup$ – Joe H Jun 12 '18 at 2:54
  • $\begingroup$ (sorry still getting used to the site) ... yes, that would seem to hold if the whole cloud were conductive, but that's not what I'm asking. Let's assume that, prior to a strike, all the air around the charged ice or water particles is not a plasma (not conducting). It appears that the average lightning bolt might have a channel diameter on the order of several cm. But the negatively charged region at the base of a storm cloud could easily be a square kilometer. So how might such a large region of charged particles instantaneously conduct into a strike? $\endgroup$ – Joe H Jun 12 '18 at 3:05
  • $\begingroup$ Yes, sorry... I meant to say "If the clouds were conductors, they would almost never discharge..." I think you may be missing my point a little. That the cloud is a giant insulator means lots of charge can accumulate over very large regions, which causes a large electric field. If the field becomes large enough, it can cause an electrical breakdown of the atmosphere, which allows the excess charge to discharge through a lightning bolt. It's the field that starts all of this, which stems from its source, the accumulation of large amounts of charge. $\endgroup$ – honeste_vivere Jun 12 '18 at 13:35
2
$\begingroup$

The strike does not happen instantaneously - it may take milliseconds for the stepped leader to reach the ground - so there is some time for the charges, spread over a large area of a cloud, to reach the discharge path.

At very high field intensity levels, common in charged clouds, air molecules are easily ionized and serve as carriers of the discharge current.

Once the discharge has started (due to a particularly strong field in some location), negative ions start flowing downwards (assuming a cloud-to-ground lighting), while positive ions flow back to the cloud. This intensifies the field at the root of the discharge channel and, as a result, the ionization spreads to the adjacent areas of the cloud, intensifying the field there, etc.

So, presumably, we have an avalanche ionization process that allows charges from significant area of the cloud to flow into the lighting channel.

$\endgroup$
  • $\begingroup$ This was exactly what I was looking for - thank you! $\endgroup$ – Joe H Jun 13 '18 at 15:23

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.