Lightning

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)

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