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Hurricane Ivan over Gulf, Sept. 2004 Source: NOAA Thunderstorms, Tornadoes, and Hurricanes October 27/28 2010 Definitions * 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. Weather VS Climate * Weather describes whatever is * Climate describes the total of all * Weather is what happens from * Climate tells us what it's usually like happening outdoors in a given place at a given time. minute to minute. weather occurring over a period of years in a given place. in the place where you live * 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 is what you expect, weather is what you get! * 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 * 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? * 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 * 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! Microburst #2: How do you think it could be dangerous to aviation? Source: Wikipedia # days per year thunderstorms observed. Do you think hail follows the same distribution? #3: How are max/min different here? Why do you think more hail over Rockies, Great Plains? * 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. http://apollo.lsc.vsc.edu/classes/met130/notes/chapter14/graphics/lightning.mpg * 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 * 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 Sept 2003, Carquinez Straits, CA After rare influx of moisture from SW Cloud-to-ground lightning over Las Vegas during SW monsoon season * 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) Source: http://www.cs.uwaterloo.ca * 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 Source: http://www.april31974.com * 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 Source: http://wximpact40-88.pbworks.com * 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 * 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 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) Be careful * 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 Anatomy of a hurricane * Convergence at surface brings warm, moist air up * Divergence aloft and sinking air outside the hurricane, clear skies immediately surrounding * 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”! #7: Why do hurricanes move from East to West? * 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 Atlantic and Pacific Storm tracks, 2010 Source: Wikipedia Source: Washington Post * 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 Source: www.katrinadestruction.com * 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! Source: NOAA * #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 Gets name when becomes TS If major event (like Katrina) name retired for several years Source: Farmer’s Almanac * 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 * 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 Source: NOAA/wikipedia * 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… Source: The Economist, Rianovosti * 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 * 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