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Extreme Weather

Hurricane Ivan over Gulf, Sept. 2004. Source: NOAA. Extreme Weather. Thunderstorms, Tornadoes, and Hurricanes October 27/28 2010. Climate Change : Changes in climate of the past, present or future associated with natural or anthropogenic (human) factors Global Warming :

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Extreme Weather

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  1. Hurricane Ivan over Gulf, Sept. 2004 Source: NOAA Extreme Weather Thunderstorms, Tornadoes, and Hurricanes October 27/28 2010

  2. Climate Change: Changes in climate of the past, present or future associated with natural or anthropogenic (human) factors Global Warming: Warming of the 20th and 21st century associated with anthropogenic activities. Definitions

  3. Weather describes whatever is happening outdoors in a given place at a given time. Weather is what happens from minute to minute. can change a lot within a very short time Weather includes daily changes in precipitation, barometric pressure, temperature, and wind conditions in a given location. Climate describes the total of all weather occurring over a period of years in a given place. Climate tells us what it's usually like in the place where you live Weather VS Climate Climate is what you expect, weather is what you get!

  4. Begin in cumulus stage • Warm, moist air rises, cools. • Water condenses out of air, releasing heat • Updrafts develop • Precipitation occurs when weight of precipitation overcomes updrafts Thunderstorms

  5. Cloud draws in drier air which evaporates some moisture, causes cooling. • This cool, dense air sinks, creating downdrafts • Downdrafts mark mature thunderstorms • Downdrafts and updrafts make the thunderstorm cell • Storm may extend to top of tropopause (~12 km) • #1: Why doesn’t precipitation fall right as condensation occurs? Thunderstorms

  6. A rush of cold air (downdraft) usually occurs at onset of precipitation • Storms usually dissipate within 15-30 min. • Updrafts weaken, downdrafts dominate • Provide summer rainfall for much of the US • Cooling of up to 10˚C/18˚F on hot summer days • Strong downdrafts can force more warm air up, causing multi-cell storms. Thunderstorm development time lapse (Florida) • http://vimeo.com/4806845 Thunderstorms

  7. Stronger winds aloft than at surface vertical wind shear • Tips over top of storm, allows for prolonged updrafts, longer storm life • Hail forms due to strong updrafts, falls when heavy enough to overcome updrafts • Strong downdrafts called “microbursts” may occur, winds up to 146 kt • Dangerous to aviation! Severe Thunderstorms

  8. Microburst #2: How do you think it could be dangerous to aviation? Source: Wikipedia

  9. Distribution of Thunderstorms # days per year thunderstorms observed. Do you think hail follows the same distribution?

  10. #3: How are max/min different here? Why do you think more hail over Rockies, Great Plains? Distribution of Hail

  11. Lightning occurs to reduce a buildup of positive and negative charges within a cloud. • + charged ice crystals tend to be at top of cloud, and - charged hailstones at bottom. • Area of positive charge on ground develops below storm • When electrical potential gradient large enough, the electrical current flows to surface as lightning! • Can have cloud-to-cloud, cloud-to-ground, or lightning within a cloud. Lightning

  12. http://apollo.lsc.vsc.edu/classes/met130/notes/chapter14/graphics/lightning.mpghttp://apollo.lsc.vsc.edu/classes/met130/notes/chapter14/graphics/lightning.mpg

  13. Can heat the air rapidly to 30,000˚C/54,000˚F • This rapid heating causes air to expand and makes a booming sound wave– thunder! • Sound takes 3 sec to go 1 km, (5 sec per mile) • #4: If you see lightning and hear thunder 15 sec later, how far away is the lightning? • 5 km/3 miles away! • Sometimes thunder is not heard due to the atmosphere bending the sound waves upward Lightning

  14. 100 people per year die of lightning strikes • If about to strike, hair stands on end, skin tingles, hear clicking sounds Source: www.goldengatephotos.com Lightning Cloud-to-ground lightning over Las Vegas during SW monsoon season Sept 2003, Carquinez Straits, CA After rare influx of moisture from SW

  15. Rapidly rotating winds around intense low pressure center • Start as funnel-shaped cloud • Diameter of 100-600 meters (300-2000 ft) • Move at 20-40 kt (23-46 mph) • Last only a few minutes • Travel up to 7 km (4 mi) Tornadoes Source: http://www.cs.uwaterloo.ca

  16. Most violent event: April 3 and 4, 1974 • 148 tornadoes over a 16 hour period • Covered 13 states • 307 people killed, 6000 injured • $600 million in damage Trailer park destroyed in Huntsville, AL F4 tornado over Parker City, IN Tornadoes Source: http://www.april31974.com

  17. Tri-state tornado event March 18, 1925 • 7 tornadoes across MO, IL, IN • 695 people killed! • US has most tornadoes of all countries • Occur in all states, greatest number in “Tornado Alley” • This is area where cool, dry air from Canada meets warm, moist air from Gulf Tornadoes

  18. Source: http://wximpact40-88.pbworks.com

  19. Tornado alley susceptible since warm, humid air overlain by cool air aloft • If strong vertical wind shear occurs and thunderstorms form, tornadoes likely • Usually occur March-July in late afternoon • Can pick up people, animals, appliances, railroad cars • 220 kt winds max, most < 125 kt • Can pop roofs off/collapse houses! (Bernoulli’s principle) • #5: How can tornadoes “pop” a roof off a structure? Tornadoes around the US http://www.youtube.com/watch?v=43VoMesUd2Q Tornadoes

  20. Fujita Scale

  21. An intense storm, winds over 64 kt/74 mph • Generally form in tropics (23 1/2˚N/S of equator) • Warm, humid areas • A “tropical” aka “Easterly” wave in atmosphere disrupts usual wind flow • In western N Pacific (Asia/Japan), typhoon • In Indian Ocean/Australia, cyclone • Today we will use “hurricane” to refer to all Hurricanes

  22. Hurricane and SST Change Webster et al. report that the number of category 4 and 5 hurricanes has almost doubled globally over the past three decades (Webster et al, 2005, Science)

  23. Hurricanes are natural events, and are not linearly related to climate change Climate change, by increase SST, indeed makes it more possible to have strong hurricane occur Be careful

  24. Anatomy of a hurricane

  25. Convergence at surface brings warm, moist air up • Divergence aloft and sinking air outside the hurricane, clear skies immediately surrounding Hurricanes

  26. Ingredients for Hurricane: • Winds light • Deep layer of high humidity, warm air • Water >80˚F • Season lasts June-November • Need converging winds, so form in ITCZ • Take in heat at ocean surface, convert it to kinetic energy as wind • Form between 5˚and 10˚N and S • #6: Why don’t they form over equator? • No Coriolis effect at equator to start “spin”! Hurricanes

  27. Hurricanes #7: Why do hurricanes move from East to West?

  28. Begins as tropical disturbance/wave • Tropical depression: winds 20-34 kts, closed isobars • Tropical storm: winds 35-60 kts • Hurricane: winds >64 kts Hurricane Katrina Source: NOAA Hurricanes

  29. Atlantic and Pacific Storm tracks, 2010 Source: Wikipedia Source: Washington Post

  30. High winds, can collapse structures • Storm surge! • High wind-driven waves • Low pressure in storm center causes sea level to rise up to 0.5 m (1.5 ft)! • Like water up a straw • Strong downbursts • Heavy, sudden rains can cause flooding Katrina damage in Mississippi Hurricanes: Why so destructive? Source: www.katrinadestruction.com

  31. August 21, 1992 • Hit Louisiana with 120 kt winds • 200,000 homes destroyed • $30 billion in damage • 53 deaths • Most deaths in US from hurricane: • 1900 Galveston, TX: more than 6,000 died! • Confused when calm eye hit, went out to “check things out”, other side of storm hit suddenly! Hurricane Andrew

  32. Source: NOAA

  33. #8: What is El Nino?What are signs it is happening? • Trade winds over Pacific slacken and/or reverse, warm water “sloshes” eastward towards coast of Peru. • Causes global climate shifts! • Atlantic: Fewer hurricanes because stronger upper level winds do not allow formation • Pacific: More hurricanes possible because more warm water over a larger area Hurricanes and El Niño

  34. Naming Hurricanes Gets name when becomes TS If major event (like Katrina) name retired for several years Source: Farmer’s Almanac

  35. Definition: A period of several days with temperatures 5’C (9’F) above average for a given location at a given time of year • Definition varies by region. • Cause 175 deaths a year in US! • During 1980 heat wave, 1250 people died! • Many more die due to secondary effects of heat • Most summers have heat waves • Heat Index- issued by NWS • Gives the “apparent temperature” combining effects of temperature, humidity, and wind • Ex, “feels like” 104’, actual temp may be 98 Heat Waves

  36. Sweating dehydrates, causes dizziness and fainting • In heat, heart pumps more blood • Blood vessels dilate • Body tries to cool blood by getting it closer to surface- can’t cool if ambient temp too high! • In high humidity, sweat does not evaporate • No cooling of skin • Also sunburn, stroke, heat exhaustion Heat Effects on Body Source: NOAA/wikipedia

  37. Temperatures up to 104’F/40’C for several weeks • Wildfires, cause poor air quality • Heat like this not seen in 1000 year Russian climate archives • 30% crop decrease expected, ban on crop exports until 12/31/2010 • 2000 people drowned trying to escape heat by bathing in rivers or lakes • Most of them were drunk… 2010 Russian Heat Wave Source: The Economist, Rianovosti

  38. Specific weather events cannot be linked to global warming • Warming and changing of Earth’s surfaces can increase probability of extreme events • Many extreme events are attributed to normal oscillations • Ex: Pakistan floods generally associated with La Nina (ENSO) summer Global Warming to blame?

  39. More areas with high Urban Heat Index • More heat waves • Warm temperatures cause more evaporation • More intense rainfall (in some areas) • More evaporation • More drought/water shortages (in some areas) • Warmer oceans • Provide more kinetic energy for stronger hurricanes • Higher and denser population • Increased chance of fatalities and damage caused by events • Especially in poorer regions without good infrastructure Global Warming to blame?

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