Transcript Thunderstorms

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)
Charges separate within cloud
thought to be due to
collisions of unlike
particle sizes
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TOP positive
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BOTTOM negative
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Induces positive charge on ground
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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