11C-1 Thunderstorms 40,000 each day on earth 40,000 each day on earth Most common violent storm Most common violent storm Small (few km in diameter) Small (few km in diameter) Form on hot summer days due to convection or on the edges of cold fronts Form on hot summer days due to convection or on the edges of cold fronts

Thunderstorms Thunderhead Thunderhead –Cumulonimbus cloud (vertically developed) –Anvil shaped on top

Thunderstorms Lightning: Electrical discharge Lightning: Electrical discharge –Cloud to cloud –Cloud to ground –Top of cloud becomes + & bottom becomes – –Voltage difference causes spark to jump

Stepped leader Stepped leader –Electricity heading down in steps Return strokes Return strokes –From ground up to stepped leader –Happens so fast it looks like 1 flash Forked lightning Forked lightning –If stepped leader branches on the way to the ground

Thunderstorms Temperature of lightning bolt is very hot Temperature of lightning bolt is very hot Forces air nearby to expand rapidly, causing thunder sound Forces air nearby to expand rapidly, causing thunder sound Speed of light & sound not the same 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 Can’t hear thunder beyond 16 km

Thunderstorms Heat lightning Heat lightning –Same as regular lightning, but too far away to hear thunder

11C-2 Tornadoes Narrow funnel cloud extending from cumulonimbus cloud Narrow funnel cloud extending from cumulonimbus cloud Narrow path of destruction Narrow path of destruction Highest speeds of any storm (515 km/hr) Highest speeds of any storm (515 km/hr) Occur all over the world, but USA has the greatest number & most destructive Occur all over the world, but USA has the greatest number & most destructive

Waterspout Waterspout –Tornado at sea (less intense)

Tornado Base Base –The part on the ground –Most destructive part –May be 1 m to 5 km (400 m average) Fujita Pearson Scale based on… 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 have several funnels from same cloud Can travel 100 km/hr on ground Can travel 100 km/hr on ground Often zigzags Often zigzags General SW  NE direction due to prevailing westerlies General SW  NE direction due to prevailing westerlies Destructive forces: Destructive forces: –Windspeed & updraft –Can lift cars, houses, etc

11C-3 Hurricanes Huge cyclonic windstorms that form over tropical or subtropical oceans Huge cyclonic windstorms that form over tropical or subtropical oceans Huge diameter (160 km to 1000 km) Huge diameter (160 km to 1000 km) km/hr winds km/hr winds Dangerous to ships & shorelines due to… Dangerous to ships & shorelines due to… –1) High winds –2) High tides –3) Heavy rains/flooding

Typhoons – hurricanes in Pacific region Typhoons – hurricanes in Pacific region Cyclones – hurricanes in Indian Ocean Cyclones – hurricanes in Indian Ocean Tropical cyclones Tropical cyclones –Form near equator –Small & violent Extra tropical cyclones Extra tropical cyclones –Form over middle latitudes –Larger but less violent

Hurricanes Require warm water Require warm water to form Usually 10-15° latitude Usually 10-15° latitude How hurricanes form 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 Saffir-Simpson Hurricane Categories: 1-5 Eye of the hurricane Eye of the hurricane –In the center of the spiral –Low pressure –Can have calm air, no rain

Hurricane over land… Slows down Slows down Loses energy due to friction with land and no longer a supply of warm moist air Loses energy due to friction with land and no longer a supply of warm moist air Wind slows  no longer a hurricane Wind slows  no longer a hurricane Heavy rains continue Heavy rains continue

Storm swell Storm swell –Huge waves produced by the high winds –Hits shore before hurricane arrives Storm surge 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 Hurricanes cause loss of life & property Safest to evacuate Safest to evacuate Hurricanes seen in advance on satellite Hurricanes seen in advance on satellite –Good tracking systems & early warning systems help, but path may still be unpredictable

Facet: Safety in storms Thunderstorms 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: Tornadoes: Best protection is 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 Hurricane: evacuate the area –Board up windows –Leave if instructed by authorities to do so Facet: Safety in storms