Thunderstorms and Lightning

And Monsoons

Thunderstorms

• Convective storm accompanied by lightning.

parcels of air heat and rise; draw in air from the environment creating strong updrafts (40 mph)

falling precipitation produces downdrafts

Hail

Hard balls of ice, at least 5 mm across; made of layers of ice.

Hailstones are caught in updraft in thunderstorm cloud; they begin to fall, but are caught again in updraft; they re-ascend, outer part freezes …and this continues

Hail formation

Strength of updraft determines size of hailstones.

7 inch monster

Amazing hail stories…

• Worst hailstorms in world in Bangladesh and Deccan plateau of India.– 1988: 246 fatalities, India– 25% of hailstorms produce stones ≥ 1 inch

(4 – 7% in US Plains)

• Can accumulate 4 ft. deep, Nebraska, 1987

• 2 fatalities US, greatest damage to crops($1 billion annually)

Lightning

• An electrical discharge from a thunderstorm.

• Can heat air to 54000˚F (5 x sun)

thought to be due to collisions of unlike particle sizes

TOP positive

BOTTOM negative

Charges separate within cloud

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Induces positive charge on ground

Lightning types

• Within clouds (80%)

• Between clouds (“sheet lightning”)

• Between ground and clouds

• “Heat Lightning” : light reflected by clouds from distant thunderstorms occurring beyond horizon

thunder

Heating and expanding of air in wake of lightning

sends out sound waves

it takes thunder 5 seconds to travel 1 mile

Lightning safety:

1. seek shelter

2. avoid conductors : pipes, stoves, wires

(metal car or truck is safe, but 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)

Warning signs of lightning about to strike:

IF your hair stands on end…..

Drop to knees, bend forward to make body small, do NOT lie flat.

Lightning can strike same spot twice.

Boy on left was struck by lightning moments after photo was taken. Boy on right gave CPR and saved him. Hiker nearby was killed by lightning.

Victims:

Carry no charge

Need: mouth to mouth

Treatment for burns, shock

Monsoons

A wind reversal system that switches from winter to summer.

Most pronounced: Asian monsoon:

seasonal reversal of winds over Asian landmass due to migration of ITCZ and positions of pressure centers.

WINTER

• Dry, offshore winds over Asia

– Siberian High ITCZ low

Cherrapunji received 87 ft of rain in 1861, most between April and October, 30.5 ft of it in July alone!!

SUMMER

• Warm, wet onshore winds over Asia bring heavy precipitation

– Indian Ocean ITCZ