Lightning

updrafts and downdrafts in clouds build static electricity
charges are distributed unevenly
* top of cloud = positive
* bottom of cloud = negative
will either be:
* cloud to cloud strike (most common)
* \cloud to ground strike
travels more than 6000 miles per second
includes several strokes, all occurring within 0.5-2 seconds
rarely, bolts initiate from top of the cloud and reach the ground
positive bolts
* top of cloud has a positive charge
much less frequent, but way more powerful
“fire starters”
“bolt out of the blue”
* can reach 25 miles away from the storm
* you think the storm has passed, but lightning can still strike

static electricity builds up in the lower cloud which induces an opposite charge in the ground
electrons are discharged from cloud, creating dimly visible bolt propagating downwards
stream of electrons moves towards the ground as a stepped ladder
stepped ladder approaches the ground, electric field increases and attracts positive streams upwards
return stroke is initiated; bright flash due to positive charge sent up to the cloud
in simpler terms…
  * negative current runs down
  * positive “return stroke” runs up
    * causes air to heat to 55,000 degrees F in an instant
  * rapid expansion of air creates a pressure wave (thunder)