Extreme Instability: Thunderstorms, Lightning

Thunderstorm Convective storm with lightning 3 stages

1. Cumulus phase Air mass expands Speed of updrafts increases Parcel of air warmer than surroundings rises as updraft draws in air (40 mph) Condensation releases heat Air mass expands density decreases Speed of updrafts increases 9000 Ice crystals 6000 M meters water 3000

At first, strong updrafts prevent rain When cumulonimbus tower is high enough Bergeron process begins and rain falls.

2. mature phase downpours and lightning Precipitation causes downdrafts of cold air, which spread out below cloud Updrafts and downdrafts

12000 m ice -26°C 9000 snow 0˚C 6000 water 3000 Heavy rain at surface

3. dissipating supply of moisture is spent, latent heat decreases downdrafts overpower updrafts storm dies….

ANIMATION

Lightning Ionosphere (30 – 40 km) is + Earth’s surface is - + + + + + + + + + Ionosphere (30 – 40 km) is + Earth’s surface is - induces in cloud droplets: - top and + bottom - - - - - - - - - - - - - - -

Charges separate within cloud As big and small particles collide : heavier (hail) becomes - lighter (ice crystals) become + heavier fall ; lighter carried up by updrafts Result: + top of cloud ; - bottom of cloud t -

Cloud bottom repels - earth’s surface induces + on ground under cloud. potential builds up; mature phase: resistance of air breaks down lightning flows to neutralize charge + - +

stroke Stepped leader Return stroke Dart leader

Return stroke follows path of least resistance; e.g., tall structures

ANIMATION

Lightning safety: 1. seek shelter 2. avoid conductors : pipes, stoves, wires (metal car or truck is safe, back of a pickup is NOT safe; cloth-top convertible is NOT safe)

Avoid: Tall,isolated objects Bicycles High areas Bodies of water Mowers or tractors Individual trees (groves are better)

Drop to knees, bend forward to make body small, do NOT lie flat. Lightning can strike same spot twice.

Warning signs: Hair stand up

Underground metal pipe

Victims: Carry no charge Need: mouth to mouth Treatment for burns, shock

struck by lightning, causing burn scars, a fractured skull and a gold chain and crucifix to melt around his neck.

thunder Heating and expanding of air in wake of lightning ……sends out sound waves (It takes thunder 5 seconds to travel 1 mile)

Hail Hard balls of ice, at least 5 mm across; made of layers of ice; Hailstones : caught in updraft begin to fall causes surface melting caught again in updraft re-ascend outer part freezes; this continues

ANIMATION