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 TOP positive BOTTOM negative + + + + + + -- -- -- -- -- -- 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