11c-1 thunderstorms 40,000 each day on earth 40,000 each day on earth most common violent storm most...
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11C-1 Thunderstorms 40,000 each day on earth Most common violent storm Small (few km in diameter) Form on hot summer days due to
convection or on the edges of cold fronts
Thunderstorms
Thunderhead– Cumulonimbus cloud (vertically
developed)– Anvil shaped on top
Thunderstorms
Lightning: Electrical discharge– Cloud to cloud– Cloud to ground– Top of cloud becomes + & bottom
becomes –– Voltage difference causes spark to jump
Stepped leader– Electricity heading down in steps
Return strokes– From ground up to stepped leader– Happens so fast it looks like 1 flash
Forked lightning– If stepped leader branches on the way
to the ground
Thunderstorms
Temperature of lightning bolt is very hot
Forces air nearby to expand rapidly, causing thunder sound
Speed of light & sound not the same– Count seconds between flash & thunder
to figure out distance (& ÷ by 3)– Sound travels 1/3 km per second– If 15 seconds, 15/3 = 5 km away
Can’t hear thunder beyond 16 km
Thunderstorms
Heat lightning– Same as regular lightning, but too far
away to hear thunder
11C-2 Tornadoes
Narrow funnel cloud extending from cumulonimbus cloud
Narrow path of destruction Highest speeds of any storm (515
km/hr) Occur all over the world, but USA has
the greatest number & most destructive
Waterspout– Tornado at sea (less intense)
Tornado Base– The part on the ground– Most destructive part– May be 1 m to 5 km (400 m average)
Fujita Pearson Scale based on…– Windspeed (estimated from damage)– Path length– Path width– F5 is highest
Tornado
Can have several funnels from same cloud
Can travel 100 km/hr on ground Often zigzags General SW NE direction due to
prevailing westerlies Destructive forces:
– Windspeed & updraft– Can lift cars, houses, etc
11C-3 Hurricanes Huge cyclonic windstorms that form
over tropical or subtropical oceans Huge diameter (160 km to 1000 km) 119-320 km/hr winds Dangerous to ships & shorelines due
to…– 1) High winds– 2) High tides– 3) Heavy rains/flooding
Typhoons – hurricanes in Pacific region
Cyclones – hurricanes in Indian Ocean
Tropical cyclones– Form near equator– Small & violent
Extra tropical cyclones– Form over middle latitudes– Larger but less violent
Hurricanes Require warm water
to form Usually 10-15° latitude
How hurricanes form– Warm, moist air rises in a low pressure
area– Cool air rushes to fill the low pressure
area– Spiral forms which funnels more air
which is moist & rises more spiral of winds
– Called a hurricane when >119 km/hr winds (tropical storm if slower)
Saffir-Simpson Hurricane Categories: 1-5
Eye of the hurricane– In the center of the spiral– Low pressure– Can have calm air,
no rain
Hurricane over land…
Slows down Loses energy due to friction with land
and no longer a supply of warm moist air
Wind slows no longer a hurricane Heavy rains continue
Storm swell– Huge waves produced
by the high winds– Hits shore before
hurricane arrives Storm surge
– Increase in sea level along shore as hurricane winds pile up water against the land
– Can cause severe flooding (esp. when added to high tide)
Hurricane Safety
Hurricanes cause loss of life & property
Safest to evacuate Hurricanes seen in
advance on satellite– Good tracking systems &
early warning systems help, but path may still be unpredictable
Facet: Safety in storms
Thunderstorms– Safest place: inside a building with a lightning
rod Special metal rod on the building that goes down
into ground, attracts lighting (lighting goes through rod not building)
– Next safest: indoors not touching metal, pipes, phones, computers
– Next safest: in a car (sit in middle, don’t touch doors)
– If outside: avoid tall objects/trees, don’t be highest in object in a field (crouch don’t lie down)
Tornadoes: Best protectionis storm cellar – Next best: basement (get under strong
furniture along southwest wall)– Next best: small windowless room like
closet/bathroom– If outdoors: don’t try to outrun tornado, find
lowest area (lie in a ditch), car under overpass is better than out in the open (stay in car)
Facet: Safety in storms
Hurricane: evacuate the area– Board up windows– Leave if instructed by authorities to do
so
Facet: Safety in storms