1. Thunderstorms and Lightning
And Monsoons

2. 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

5. 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

6. Hail formation

10. Strength of updraft determines size of hailstones.

12. 7 inch monster

13. 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)

14. Lightning An electrical discharge from a thunderstorm.
Can heat air to 54000˚F (5 x sun)

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

16. 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

17. thunder Heating and expanding of air in wake of lightning
sends out sound waves
it takes thunder 5 seconds to travel 1 mile

18. 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)

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

21. 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.

22. 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.

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

24. 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.

28. WINTER
Dry, offshore winds over Asia
Siberian High ITCZ low

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

31. SUMMER Warm, wet onshore winds over Asia bring heavy precipitation
Indian Ocean ITCZ