Lightning and thunder are electrifying phenomena in thunderstorms. They result from charge separation within clouds, creating powerful electric fields. Understanding their formation is key to grasping the intense energy unleashed during these storms.

Safety is paramount when lightning strikes. Knowing when to seek shelter, avoiding risky outdoor activities, and taking indoor precautions can save lives. This knowledge connects directly to our broader study of thunderstorms and their hazards.

Charge separation in thunderstorms

Collision-driven charge distribution

• Charge separation occurs through collisions between ice particles and supercooled water droplets in strong updrafts
• Upper portion of thunderstorm cloud becomes positively charged while lower portion becomes negatively charged
• Graupel (soft hail) falls through cloud and collides with smaller ice crystals, playing crucial role in charge separation
• Earth's surface beneath thunderstorm develops positive charge in response to negative charge at cloud base
• Electric fields within cloud intensify as charge separation increases, leading to dielectric breakdown of air

Lightning formation process

• Stepped leader propagates downward from cloud in series of short, branched segments
• Negatively charged channel moves towards ground in discrete steps
• Upward-moving positively charged streamer connects with stepped leader when it approaches ground
• Connection completes electrical circuit resulting in lightning strike
• Process can repeat multiple times within a single flash (return strokes)

Types of lightning

Cloud-to-ground lightning

• Most common type observed from ground, transfers charge between cloud and Earth's surface
• Negative cloud-to-ground lightning accounts for about 90% of CG strikes
• Positive cloud-to-ground lightning less frequent but typically more powerful
• Spider lightning travels horizontally along base of storm cloud before striking ground
  • Can cover large distances before connecting with ground
  • Often visible as spectacular branching patterns across sky

Intra-cloud and inter-cloud lightning

• Intra-cloud (IC) lightning occurs entirely within single cloud
  • Appears as bright flash illuminating cloud from within
  • Most frequent type of lightning discharge
• Inter-cloud lightning travels between two separate thunderstorm cells
  • Can create impressive visual displays connecting distant storm systems
  • Helps redistribute electrical charge across broader area

Other lightning types

• Cloud-to-air (CA) lightning originates in cloud and terminates in clear air surrounding storm
  • Also known as "bolts from the blue"
  • Can strike ground at distances of 10-15 miles from parent thunderstorm
• Ball lightning appears as luminous sphere persisting for several seconds
  • Rare and poorly understood phenomenon
  • Reported to move erratically and pass through solid objects

Lightning and thunder

Thunder formation and propagation

• Thunder produced by rapid heating and expansion of air along lightning channel
• Creates acoustic shock wave that propagates outward from lightning strike
• Speed of light (approximately 3 x 10^8 m/s) much faster than speed of sound (approximately 343 m/s at 20°C)
  • Causes delay between seeing lightning and hearing thunder
• Thunder typically heard up to about 10 miles (16 km) away from lightning strike
  • Depends on atmospheric conditions and topography
• Characteristics of thunder (duration, pitch) provide information about length and shape of lightning channel
• Multiple thunder claps from single lightning strike caused by sound waves traveling different paths to observer

Estimating storm distance

• "Flash-to-bang" method used to estimate distance of thunderstorm
• Count seconds between seeing lightning flash and hearing thunder
• Estimate distance to lightning strike in kilometers by dividing time delay (in seconds) by 3
• Estimate distance in miles by dividing time delay by 5
• Example: 15-second delay between flash and bang indicates storm approximately 5 km or 3 miles away

Lightning safety

Seeking shelter

• Enter substantial building or hard-topped vehicle when thunder heard
  • Indicates lightning close enough to pose threat
• Follow "30-30 rule" for thunderstorm safety
  • Seek shelter when time between lightning and thunder 30 seconds or less
  • Remain in shelter for 30 minutes after last thunder heard
• Avoid open areas, hilltops, and isolated tall objects (trees, poles) when outdoors during thunderstorm
• Stay away from water bodies (swimming pools, lakes, beaches)
  • Water excellent conductor of electricity

Indoor precautions

• Refrain from using corded phones, electrical appliances, and plumbing during thunderstorm
  • Lightning can travel through these systems
• Avoid contact with concrete floors and walls
  • May contain metal reinforcing bars that conduct electricity
• Unplug sensitive electronic equipment to protect from power surges
• Close windows and blinds to prevent glass shards if lightning strikes nearby

Outdoor safety measures

• If caught outside with no safe shelter nearby, adopt "lightning crouch" position
  • Squat low with feet close together, head tucked, and ears covered
  • Minimizes contact with ground and reduces risk of direct strike
• Immediately move to lower ground if hair stands on end
  • Indicates lightning strike may be imminent
• Spread out if in group to reduce risk of multiple casualties from single strike
• Remove metal objects (jewelry, watches) which can attract lightning