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

A Single Flash of Lightning

• 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)